@lololulu19 It all boils down to 4k textures.
You see, for videogames to look good each object requires a few textures which are Color Map, Normal Map, Roughness Map. So you need 3 images per material.
And yes, they've been using this for years, so what changed? The main culprit is 4k and High Resolution. As an idea a single 4k texture can range between 5mb-20mb. So the textures of a single object might be around 30mb. And a reminder that big objects might need more than a single material.
We also need to consider how much bigger games are nowadays, and how many objects are in each scene. And that's how games get to gigantic amounts.
To reduce that the designers could either drop texture resolution, which would result in blurry low res textures, or do a lot of compression, which would increase load times.
3D models aren't very heavy, but in the amounts they use, it does occupy a hefty amount. Now programming barely occupies anything.
And yes, lack of polish does help increase the size of the videogame, but even a very well polished game like Baldurs Gate 3 occupies 150GB.