Thundercats Fan Trailer

Why is it that some fan made trailers get more views than the actual real trailers for movies? Maybe it's because they kick ass like this one for Thundercats movie which isn't even green lit yet. Fans will be fans. And some not so good like below But between them they have gathers 2M views. I think all studios should encourage fans to create trailers for films that have only just been announced. Why not get the marketing started as early as possible? Especially now with so many movies being made from video games, books and TV shows. They all have fan bases waiting to see something visual.