For the longest time, AAA studios mostly released simple first person shooters with straightforward enemy AI and simple physics. And Bethesda and Obsidian released gloriously buggy RPGs. Nowadays, every game includes open world elements, RPG elements, and more complicated NPC interactions... and it turns out that they are all full of bugs. Complex games have complex problems that don't reveal themselves until players do weird things.

Not to mention all these RPG systems add a whole additional layer to mess up -- character stats might not be 'buggy' exactly, but they might be very poorly 'balanced.' It is really easy to not explore every skill interaction and sometimes multipliers end up exploding. I mean, we saw Blizzard fail to balance Diablo II for like a decade or so, Wizards of the Coast tries to balance D&D but that takes all the fun out of character building -- RPGs of any significant complexity are I think just fundamentally prone to exploding numbers.