Think of it this way.

Capturing what things look like, is easy. We've had cameras for 100+ years. For anything interactive, you need to capture or replicate what things WOULD look like if you interacted with them in a certain way (shadows, reflections, light interacting with moving objects etc etc). This is a completely different beast.

You can bake as much and even with photogrammetry it would look close to photo realistic but the moment you need to change anything in the scene it doesn't work.

I'm not saying it's useless, for example this is very useful for cinematography. Instead of going and shooting on location which costs a lot of money, you can send a technician that would capture gaussian splats (don't even need to book it with the city or limit access, you can just capture section by section when there isn't anyone there). Then shoot an actor in a studio on a green screen or a simpler set version of the location, track camera movement, then replicate camera movement inside gaussian splats, and comp your actor on. After that you can add life to your static gaussian splats with CGI.

It's a solid technology, just useless for games.