A med chemist can sit down with a known drug, and generate 50 analogs in LiveDesign in an afternoon. One of those analogs may have less CYP inhibition, or better blood brain barrier penetration, or slightly higher potency or something. Or maybe they use an enumeration method and generate 50k analogs in one afternoon.

But no one is going to bring it to market because it costs millions and millions to synthesize, get through PK, ADMET, mouse, rat and dog tox, clinicals, etc. And the FDA won't approve marginal drugs, they need to be significantly better than the SoC (with some exceptions).

Point is, coming up with new ideas is cheap, easy, and doesn't need help. Synthesizing and testing is expensive and difficult.