There's just *so many* little things like this where 1,000 teams have spent two weeks doing something poorly for want of one developer taking the ball and running with it. ("Shouldn't this be OSS?" It's the perfect example of where OSS doesn't really help you, because backend.)
Character limits are hard. You want to be able to consume file uploads as infrastructure from a program written in ~anything but OSSing them requires you to run and administer (monitor, update, etc) some backend service, which minimizes the utility of the OSS frontend.