Languages were simpler (except for certain ones, like C++ which was a beast even in 1992), and incredibly complex and magical optimizers weren’t yet a thing, never mind a feature expected of a "passable" compiler. One could still write a reasonable non-optimizing Pascal or C89 compiler in a weekend more or less, and it would be both faster to write (thanks to more expressive languages) and faster at compiling (thanks to itself being compiled by an optimizing compiler) than in 1992!