I think it's because Smash has a huge black fanbase and black people LOVE LOVE LOVE Dragonball.

Heck, they refer to Lucario as Black Goku.

Otherwise, Dragonball is probably the most famous fighting characters in all of media, so it's not unexpected that they would be requested in any fighting game that has a slim to chance at all of them joining. If Marvel vs. Capcom brought in any other franchises, you can bet that they would then be instantly flooded with Goku requests. If Soul Caliber brought in random people like they did back on Dreamcast with Link and others, you can bet they would be flooded with Goku requests. Ect.

Seriously?! I guess now that Ridley's out of the way we're gonna have to deal with people begging for Goku?

Listen, it ain't happening. Goku is a manga character first and foremost, his appearances in video games is not even secondary. Theirs also the fact he hasn't had as big of an influence as any other character on the roster (outside of maybe Ice Climbers but they're a retro character) and i'm not talking cultural or shoenen, I mean video games. What has Goku contributed to video games? Maybe a good fighter or 2 but nothing else. He's had no impact, he's not a part of the classics and he's not a video game or Nintendo character.

Stop with this meme of wanting Goku in Smash. It's the worst crap i've ever seen! Worse then Ridley, worse then Waluigi, worse then Shrek! At least with people that say they want Shrek, I knew were just joking.

I dont disagree with most if not all with qhat you said. Im looking at it as what can Sakurai do in terms of WTF impossible character to add to the game. In Brawl it was a third party character that has history with Nintendo. In SSB4 it was Cloud who ever was like WTF he never be in the game. Hell you can say Bayonetta as well

I feel like this game out of rule character would be Goku. Im not expected it, but i dont think its impossible is all im saying. Its definelty a less than 0.1% but above 0.0% :p

It is more likely given the buddy relationship Nintendo and Bandai Namco have. I mean they threw Xenosaga characters into Xenoblade 2.

I don't think the creators of Goku would want to see him being beaten up by jiggly puff or princess beach lol.

I like Goku as a fighter (though not much as a father) as the next guy, but I'm not gonna hold my breath of him getting into Smash. Yes, Bandai Namco is working on the game with Sakurai and they have made the DBZ games for a long time. Yes, Goku has made several video game appearances. However, I'll give Goku as much of a chance as a PlayStation first party character has, very little. I recognize Goku as an anime/manga icon, ultimately. Plus, even if he does get in, would he be the Goku that you wanted as a fighter? Goku is notably pretty powerful, but Sakurai would have to make some pretty big compromises with some of his moves, including the Kamehameha Wave, the Solar Flare, Instant Transmission, and his transformations such as Super Saiyan, Super Saiyan God, etc. How would it affect the other characters on the roster? That is part of Sakurai's criteria when deciding on a moveset for characters.

https://kotaku.com/smash-bros-creator-explains-how-characters-get-on-the-1644208199

For the most part, all the characters represent the basic core foundations of themselves and not necessarily the best version of themselves. How do you best remember Kirby in his most basic form? A puffball who can suck opponents and use their respective powers against them. What about Lucario? An Aura Pokemon who gets stronger as the battle goes on. What about Link? An adventurer/warrior who wields the Master Sword, Hyrule Shield, Bow and Arrow, boomerang, and bombs. If you had the best versions of themselves, then Shulk would be "spoilers," Kirby would be a small black hole, Palutena would actually do more than what she's shown in Smash as the Goddess of Light, Mewtwo would utilize his Mega Evolution forms more, etc. With all that has happened around Goku, would you really want him to be just sticking to his original form with some of his most basic moves such as the Kamehameha Wave? Not as interesting as giving him transformations such as Super Saiyan God or what not.

Gen 6 had new Megas within the same gen that were only available to Omega Rubr/Alpha Sapphire players, and Gen 7 debuted Blacephalon, Stackatacka, Zeraora and Dusk Lycanroc mid-gen, albeit on new SKUs. Anything is possible. 

Why the hell not!? Spawn made an appearance in Soul Calibur.

Pretty much this. I take those requests as serious as the ones for Shrek.

Smash Bros was originally thought to be a celebration of Nintendo/1st party titles. As such, only Nintendo/1st party characters cpuld be allowed. That notion died when Snake was revealed for Brawl. Since then we have had Sonic (Mario’s rival), Mega Man, Pac-Man, Bayonetta, and Cloud Strife (one of the PS1’s mascots). I’m almost certain that Crash will be revealed before the game releases too. Now Smash Bros. has become known as a celebration of gaming in general, not just Nintendo.
My question is: Why stop there?

When you already have nearly all of gaming’s most iconic characters in history, where do you really go from there? Including iconic characters that are outside of gaming is the next logical step to make the series a bigger deal than it is. Although, I don’t think Goku is the character you have that gargantuan reveal for, I think that would be Mickey Mouse. Because, come on! Mickey Mouse and Mario beating the crap out of each other? Who wouldn’t want to see that?!?
And from that point on, Goku would only be a matter of time. In fact, it wouldn’t surprise me if he was the next one.