Everyone always talks about Crash and while he'd be super cool, no one ever gives Spyro any love here...
I'm a fan of Spyro too and would be cool with him in Smash... But not before Crash Bandicoot and most fans of both characters/franchises would likely agree if we are trying to be "Realistic".
Let's be honest while both were the 1-2 punch platforming mascots on the Playstation during that era, Crash Bandicoot was and still is the bigger name of the 2, Hell Crash got spinoffs in the form of a Kart racer and Party game outside of the original trilogy which says a lot about the brand power of the franchise at the time something that Spyro never got despite the franchise's success too.(Spyro appearing as a guest character in Crash Bandicoot's world via Nitro Fueled further cements that too.)
Also just like many have mentioned before Crash Bandicoot has the advantage of being one of the first and few western IP's that actually was popular and caught on in Japan/East, Unfortunately the same can't be said for our purple dragon friend. (While not necessarily required, It certainly helps)
Other Minor Details/Advantages:
Let's not forget that Crash Bandicoot was the 1st of the 2 franchises to debut and establish himself as the face of the Playstation brand back in 1996 and the trilogy wrapped up with "Warped" in 1998 the same year Spyro was just barely about to make his debut.
Also because of their origins and ties with Sony and Universal at the time Spyro's demo can also be unlocked in "Warped's" Menu so in a way Crash Bandicoot helped introduce Spyro the Dragon to many young gamers for the first time too.
It would be great to get both into Super Smash Bros Ultimate, But chances are it's gonna be first and likely only Crash, The only way I can see Spyro making it in is if Nintendo and Activision struck an "Ultimatum" deal that they have to include both or nothing, While possible, I just don't see Activison being that stubborn to let that happen.