I assume that a game developer could theoretically recompress textures, either on the fly, or on first run, or provide multiple texture packs (ultra, high, medium..) to fit in the available memory but if they are lazy then you have a problem.
Say you build a game around one of the most common VRAM sizes 8GB (most people dont have anything above), some of it will be allocated to textures, but other partitions of the budget will be allocated to frame buffers, vertex/indices data etc... It's a business thing. Spend enough time to make it look great, and make it run fast enough to sell without complaint, VRAM budgets enable that.
The only time usually a VRAM budget will exceed 8GB is if one of three conditions are met; either the developer didn't stick to the budget (rushing a game to market cough cyber cough punk), a resolution large enough to exceed the budget is chosen (say 8k), or there is enough available VRAM to move up to the next larger budget. I'm going to make a wild guess, but I don't think most games companies focus on budgets over 12GB, so the 24GB is mostly wasted as if you had all 3 conditions met, you'd still barely scrape 14-15gb used in big titles, Doom Eternal etc...
Interestingly on the lower end some companies more recently tend to skimp out on smaller budgets. Say you've got a 2GB dinosaur and can't boot a game due to a "not enough vram" warning, now you know why low texture packs exist.