We've asked YouTube for comment.

It's not clear at this stage why YouTube might pull the web app. Android Police speculated that this could be an attempt to discourage device makers from circumventing its app through a browser. However, it could also just be a matter of shifting company resources as the web version becomes less and less necessary. Many people now have access to smart TVs, consoles and media hubs with a largely identical interface. In those cases, the web version is redundant. This could help YouTube pour more effort into native apps.

Update 9/16 1:38PM ET: YouTube declined to share more beyond confirming the shutdown, but a Variety source said the interface will shut down on October 2nd.