Why can't there be two consoles/handhelds in the same generation? You make it sound like there can only be one. If the Switch Successor is released in Spring 2025, then I would consider it as 10th gen.

I think the main reason people consider Switch as gen 8 is because there weren't any big consoles to release in 2017. 2017 had New Shield Android TV, Switch, New 2DS XL, SNES Classic, Xbox One X. New 2DS XL, and Xbox One X are upgrades. New Shield Android TV is too small to be noticed. SNES Classic was a "reboot"? No other generation has a 3 year gap between big console releases, so people just put it in as a very late gen 8 release.
There's the bias reason, where the gaming community doesn't view Nintendo as a big contender or want to downplay the Switch hence why its gen 8. (This reason is more of a speculation).

I have no problem saying that the Switch can be gen 9, but I do see what are some reasons for gen 8 placement.

I voted 10th gen just because it seems like Switch 2 isn't coming until 2025. Also seems like PS6 will possibly be 2027 and the next Xbox 2026. So Switch 2 will be primarily competing with and existing with those two consoles.

With that said, I've kind of given up on what gen Nintendo hardware is in considering there's no consensus on what gen the Switch is in and I expect this to continue with Switch 2.

I think it's time to dispense with the idea of generations. Microsoft wanted to get rid of it several years ago, but they didn't have the market clout to make it happen. It looks like they are continuing to move in that direction though, just less overtly. Release schedules aren't matching up, at least between Nintendo and the other two. But, I think it's highly likely that the 9th generation is also the last time that Microsoft and Sony have launch schedules that align.

Then there's the fact that the gaming market has grown tremendously, beyond the old dedicated hardware model, and even the three players that are responsible for hardware in the traditional portion of the market are starting to differ in the ways that they want to serve that market. So there really just isn't much point to put them into a generation group anymore. Microsoft doesn't care about selling consoles. Nintendo is selling lower tech, portable hardware. Sony is really the only one still trying to sell traditional, relatively high power, video game hardware.

Grouping them into a generation for purposes of discussion may have made sense in the past. I guess it kind of still makes sense today. But, it's usefulness is quickly dwindling.

That has happened several times in the past.

See: Atari 2600 and Atari 5800.
See: Xbox One and Xbox One X.
See: Playstation 4 and Playstation 4 Pro.
See: Xbox Series X and Xbox Series S.
See: PSP 1000 vs PSP 2000, 3000, Go, E1000.
See: 3DS and NEW 3DS.
See: DS vs DSi.

They often feature faster CPU's, GPU's, more RAM, more storage etc'.

The Xbox One and Xbox One X differ even on chip architecture somewhat. - Aka. AMD Jaguar CPU cores vs Jaguar Plus CPU cores, DDR3 vs GDDR5, eSRAM vs no eSRAM, Graphics Core Next 2.0 GPU architecture vs Graphics Core Next 4.0 GPU architecture.

Yea that is very true. And apologies, I was referring to new consoles (I personally have those as upgrades), but yes you are correct. Thank you!

It hit the 5 year mark so yes 10th gen.