Why is there an in-game photo cap?

...performance reasons most likely. It takes longer to load the more mods there are and they're (probably) trying to account for lower end systems ("idiot proofing"). Or there's a point where it would simply just crash with the way they have it set up, who knows. Plus they couldn't make the in-game thing work/sync properly with 50 (the sample-pics in mine get all messed up/inaccurate after maybe 20 or so).

That said, it's the kind of thing they could have put in some options, like "20, 50, 100" for those with higher end rigs/user choice.