> In GoldSrc lightmaps cannot get more intricate though, they're tied to the texture scale so you cannot get a finer lightmap unless you also make larger textures and scale them down, and these two combined will wreck your "AllocBlock" budget in which all your textures and lightmaps must fit.

AFAIK some of the improvements include much better light bouncing techniques, transmission of surface colors like source does, more accurate lights, spotlights that emulate what source spotlights does and faster compilation (computers also got faster and MT support helps a lot). That alone allows level designers to be more ambitious by taking advantage of faster iteration and place even more lights.

I do agree that there are likely dozens if not hundreds of reasons why maps can and usually do look way better today than what could be done in the past. Hell, even level designer proficiency with the tools as time goes is also surely a reason.