Improvements in development/debugging tools definitely explains part of the puzzle - but I think your last sentence is actually a much better explanation, because I absolutely remember games where cheats weren’t just in the game, but were explicitly available to the player through menus (the Ratchet and Clank quadrilogy comes to mind).

The culture around cheats has kinda just changed. People much more value either a vanilla single-player experience, or a truly modded one. Plus the prevalence of multiplayer games has increased exponentially since cheats were popular - and of course outright cheating online is a big no-no (though I wish that were the case with P2W)