For example, if in year N youtube has f(N) new video. Let assume f(N) = cN^2. It's a crazy rate of growth. It's far better than the real world Youtube, which grew rather linearly.

But the rate of "videos that are older than 5 years" is still faster than that, because it would be cubic instead of quadratic. Unless the it's really exponential (it isn't), "videos that are older than 5 years" will always surpass "new videos this year" eventually.

Such a weird strawman argument that you are making up. You've over thought this so much that you are missing the forest from the trees

Maybe it could be used to train a neutral network. Maybe it contains dirt on a teenager, who might become a politician two decades from now. Maybe it contains an otherwise lost historical event.