First, because it is silently implied that all good websites should collect and check the official IDs of all good citizens uploading any data to them (what a great perspective)...
There's a significant difference between "uploading any data" and "uploading porn". Suggesting someone who is uploading porn should have to prove that they're entitled to, and that the people in the video have consented to be put online in the context of a porn video, is not unreasonable given the weight of evidence that "revenge porn" is incredibly damaging to victims.
There's a significant difference between "uploading any data" and "uploading porn". Suggesting someone who is uploading porn should have to prove that they're entitled to, and that the people in the video have consented to be put online in the context of a porn video, is not unreasonable given the weight of evidence that "revenge porn" is incredibly damaging to victims.