It's a rather brilliant idea really, but when you consider the environmental implications of forcing web requests to ensure proof of work to function, this effectively burns a more coal for every site that implements it.
But when you consider the current worlds web traffic, this isn't actually the case today. For example Gnome project who was forced to start using this on their gitlab, 97% of their traffic could not complete this PoW calculation.
IE - they require only a fraction of computational cost to serve their gitlab, which saves a lot of resources, coal, and most importantly, time of hundreds of real humans.
I don't think AI companies care, and I wholeheartedly support any and all FOSS projects using PoW when serving their websites. I'd rather have that than have them go down