Why do people think UFC is the only MMA promotion with good fighters?

Some of the top 25 fighters in the world aren't even in UFC. Dominick Cruz in WEC, Alistair Overeem in Strikeforce, Eddie Alvarez in Bellator and etc. Heck UFC wasn't all that famous until they got all the best fighters from PRIDE in Japan. So my question is why do people think you will only find the best MMA fighters in UFC only?