There was no other, simpler interface. And the whole system was much simpler (and less capable). The graphical hardware was way simpler and fully in-house, unlike the current GPUs that are third-party and evolve quickly.
Exactly, there was no other, complicated interface. Except in 1991-1995 when System 6 was going to merge with AIX and be A/UX and Apple was going to merge with IBM and it was all briefly very weird.
