Which causes more people to watch it, which increases the odds someone posts it to a different site and also increases the odds someone on that third site has already seen it and comments, etc. etc. A big surge in one site can affect multiple sites pretty easily, especially if they share a large proportion of their user base and/or users can easily bounce between them even if they're not regular users of one or the other. It's kind of tin foil hat territory to assume it's a "coordinated push" and not just how "the algorithm" + the internet works in general.