I think they would if the mobile phone app started uploading a bunch of content and eat into bandwidth and battery. If the app doesn't upload, we still have a centralized system with a very inefficient transport layer.

Besides, even if you work around that problem somehow, YouTube has an insane amount of videos with very few views. That means there are not enough people to upload content, the centralized server or the original uploader needs to keep hosting them.

if it did collapse from a YT clone, IPFS was not set up to handle what we really need it for, firehose science data sources.