It’s not just a divide of popular games and unpopular ones.
There’s also a divide of budget. Lower budget games are more likely to have worse QA with more glitches remaining at time of release. Higher budget games, hopefully less so.
There’s also a divide of newer vs older games. Older games are simpler pieces of software, built using old tools, running on simpler platforms. Often times they were written from scratch in C or even assembly. It’s more likely for them to contain serious bugs, and they are easier to find due to decreased attack surface. Then again, sometimes older games are so small and simple that they are basically bulletproof. Pac-Man might crash when the score gets too high, but there’s no magic glitch to do that instantly. You have to get good.
And yet again there’s a difference of game engines and development tools. Building a game with a modern game engine already puts the weight of so much QA behind the software before development even starts. Sure there might be some out of bounds or something, but finding a magical way to skip to the end of the game will be difficult unless the developers were extremely negligent (or it was intentional).
Even in the cases where there isn’t some ridiculous glitch to skip the entire game, any% runs of almost all games include some exploitation that was not developer intended. Consider the Castlevania SotN any%. There’s no magic glitch to make the end credits roll, but there are some absolutely ridiculous tricks that are basically cheating. The any% world record is about half of the glitchess run.
Speedrunners recognized and solved this problem long ago. The way I think about it is this:
Glitchless is trying to play the game as fast as possible.
Any% is trying to play as little of the game as possible.