Because that's the way they designed it. I don't know why people apparently think a computer can weigh options, have an opinion & use better judgment. Programming scripts are comprised of nos, yeses, ifs, ands & buts, not maybes. If the parameters of a claim fit within a certain condition, an "if" script has been fulfilled & it will perform the intended function.
Not only that but what motive does Youtube have to really be proactive about this? It's ultimately no skin off their ass. Their #1 concern is their own safety. You could argue that it wastes more of their time but you're also asking them to redesign their script, update it across all their servers all to accommodate a niche market on their site that they actively booted off in the mid 2000s.
I don't think this is exactly a major priority to them.