Are you sure? Google has been on a kick for some time now to try and ensure each product area is independently profitable. Up until a few years ago the status quo was that search/content ads made all the money, and every other product burned it in a giant furnace of endless massive losses. Seems they're now trying to get a grip on that as they're realising even search ads can't keep growing revenue forever.

It's entirely possible that YouTube has never been profitable. The costs involved with it are stupendous. It's far more than just bandwidth. Storage and CPU for transcoding, the enormous databases required for Content ID, recommendations, comments and anti-spam, all the private videos you can't even see at all, etc. Then there's software development costs to manage the bandwidth and operations.