I'm guessing there may be resoure issues for the admin, as they have to pay for the server's costs?
If you want to post long high quality videos I'd recommend using PeerTube instead. PeerTube accounts can be followed and interacted with from Mastodon, but PeerTube has a much better way of handling high bandwidth files.
For example @theatticdwellers is a PeerTube account, if you reply to its posts the replies will appear as comments below that video on PeerTube.