While it's a different niche, the worry for YouTube is that younger viewers generally consume a lot of short form video. They might eventually shift to watching more long form content as they get older, but if they're accustomed to one provider it's going to be easier for that provider to expand into long form content than for YouTube to persuade them to switch or use a second provider. So YouTube feels it has to move into short form in order to ensure long term maintenance and growth of its user base.