Less triangles and smaller textures. Crt monitors had less resolution and practically built-in anti-aliasing so they could get away with (and had to) "worse" assets.

Also since ssd-s have become mainstream unity uses less compression so it would load relatively faster.

Basically because monitors got better, standards got higher, competition got fiercer, storage got bigger and faster, etc.

And it's not like there weren't shitty games before, just everybody forgot about them.

I like how the game Banished is made. From a requirenments/looks ratio it is IMO great. One guy made it. Ghosts of Tsushima also looks amazing and is great from a techical perspective, but it is heavy.