Partially the continuous growth of polygons, quality and size of all data together.
But also a big part because over the years they can no longer throw off file sizes because with large hard drives / SSDs it is possible to write up to 150GB without causing problems.
In the past, when everything was still on CD / DVD and you couldn’t assume your customer had downloaded at least 100MB, you just had to get everything on disk, and it couldn’t be duplicated with the day1 correction due to the 1 replacement texture became Also a substitute for all textures.
Often the patches were just MBs, and at worst you’ll have one in hundreds of megabytes in between, but this mainly happened on a PC rather than a console.
Then there was the high-speed internet and Blu-ray + consoles that had ample storage. And then it was no longer interesting for developers to wind up things with all sorts of tricks. It takes time, makes the game load a bit slower, and there’s a lot of space available, why bother.
And now it’s over the top (especially since many games now come in 4K texture, on disk whether as an update that you can share immediately upon startup or not) that you will have to install 500GB + games on your disk because no one at Activision knows how to compress files efficiently. To save space … No, let’s force players to upgrade their system! 
Everything has gotten so crazy.
