Understandable opinion :).
There are several layers here. First the original backgrounds were proprietary images, which we cannot use, so they had to be recreated with AI already. Also the new images are heavily edited to maintain map continuity, mainly the beach and hideout ones.
Secondly it is a compromise, as you said, the game is free and we ain’t going to waste money on backgrounds when there is so much CGs to purchase. We are not artists and people don’t readily offer their work for free, so you have to pick your fights.
One could argue that we could use free backgrounds, but that would introduce a few problems hard to solve like, consistent art style, map continuity, freedom to edit them given licensing and finding the right backgrounds for the right places.
Then again, I totally understand, I also don’t like to use AI for major roles and art pieces and that’s why it is only used on the backgrounds.