After showing this to another person they said

"The downfall of any major company doesn't happen after a single failed product (dreamcast)
For sega to have exited the console race will have taken many more years of failure then just the 4 or so years the DC was on the market.
In light of that, nintendo weakened the pillars and then the ps2 delivered the killing blow"

It also doesn't help that sega built those pillars out of chocolate. So yeah really it was on sega

Sega never had a firm foothold in the console market to begin with. Their only successful console was the Genesis, which still ended up losing to the SNES. They also squandered a lot of goodwill with the 32X and the Saturn. Their most successful console in Japan was the Saturn, which was an abject failure everywhere else in the world.

Sega and Sony are obviously the most involved in the fall, but I'd say Nintendo at least got the ball rolling with the ferocious console war, like little that's ever been seen. The main difference is I don't think Nintendo ever gave Sega any serious wounds, just if anything kept Sega trying to fight them and otherwise make errors trying to overcome them. But a 32X doesn't kill you, but it can start the death roll.

Sega

Sega is the one responsible. Had they not been so mismanaged (in Japan; the US branch were borderline geniuses), they would have gone on to become what Sony became. They had entered the console market when Nintendo had over 90% of the marketshare in the US (1988), and by 1993, they were winning. But the people in Japan who owned the company decided to take the reigns back and started making horrific decisions that all but sealed their fate. Sony stepped in, took the opportunity that Sega had provided, and capitalized on it. But make no mistake, Sega killed Sega.

While I think Sega made some huge mistakes, so did Nintendo with the N64, Gamecube, and Wii U and they survived. So I don't think Sega is ultimately completely to blame for their own downfall. Sega had a lot of momentum, I had quite a few friends that had the Genesis, when the Playstation came out I never heard anything about the Saturn among my friends. Sure I saw Panzer Dragon demos in stores and read a little bit about them in magazines, but the mid to late 90's all of my friends talked about in the world of video games was Sony and Nintendo. I believe Sony's arrival (or Nintendo's rejection of Sony resulting in them entering the market) did Sega in. I do remember a solid launch of the Dramcast when my friends talked about the system for a few months than those talked stopped pretty quickly.

The majority who took the poll chose Sony as they were the ones directly responsible for Sega finally deciding to exit the console hardware market but it really was Sega themselves who caused their own downfall years prior. Just from the onset of the Saturn release, making the hardware cumbersome while also powerful that very few were able to really utilize it. This was just one of many missteps just like the 32X and the proposed Neptune. It wasn't just one bad decision, it was several over quite a few years. Saturn was a great platform and the bulk of the successful titles were left in JP. Whose idea was that??? Had they localized many of the games, the Saturn could have held on longer and build up a report with the users instead of its plug being pulled so quickly with the DC coming out.

Dreamcast is a fantastic way to go out. It did things even the PS2 couldn't but one aspect they could never get around was the DVD. Sony made it very easy for people to buy into the PS2 even if they never intended to play a single game on it. Sony marketing pretty much told people to hold off buying any other next gen (at the time) platform because PS2 was coming with DVD movie support... and it worked. I knew of many who just ignored the DC and its plethora of quality titles in 99 and waited until 2000 for the PS2. They didn't care that the early games didn't even take advantage of the DVD capabilities or weren't as polished as the DC titles. And so that train kept rolling and DC sales declined. EA might have kept the DC alive for a bit longer but due to their mismanagement of the Saturn, EA had given up on Sega and weren't about the go back, no matter how good the DC was. So Sega had to come up with their own sports titles (which i find to be more enjoyable than EA).

And again, bad decision making kept certain games from being released outside of JP. Sony was paying for all kinds of exclusivity before the DC launch like Tomb Raider 2 and Resident Evil 2. You ask people to pick who was the most responsible but don't even include who was actually responsible. It looks like you would rather blame an outsider instead of who really was responsible... SEGA.

It was mainly on Sega's leadership, but I would say the PlayStation. The Dreamcast couldn't even kill off the aging PlayStation and the PlayStation 2 killed the Dreamcast. The Dreamcast was discontinued only about a year after the PS2 launched in Japan, and about half a year or so after its launch in other major markets.

The Dreamcast had so much going for it, but bad blood between Sega and consumers and the sheer titan that was PlayStation killed the Dreamcast before the GameCube and Xbox even launched.

The games I saw back in the day on SEGA devices felt more edgy, and Nintendo wasn't edgy even in their "now you're playing with power" era, whereas PlayStation was always edgy, so I think PlayStation replaced SEGA as the main Nintendo rival, after SEGA had replaced Atari as the main Nintendo rival, and before Microsoft replaces PlayStation as the main Nintendo rival in 7 years after the PS6 tanks out of the gate due to $80 games and no true competition to Gamepass.

Im going on a limb by myself here, I believe that there’s enough room for 3 consoles. No matter how bad a company messes up, they can recover if there’s a market that will buy their products.

Sega had investors, their own president flushed them with all of his own money before he died. If it was just PlayStation 2 vs Gsmecube, Dreamcast could have stayed in the fight! Once the word got out that there would be 4 home consoles, that’s when Sega’s poor performance became too big of an issue. There was no market left for them to share.

I can’t envision a market that only had PlayStation 2 vs GameCube. Microsoft’s entrance is the nail in the coffin.