Why do NBA teams get so excited about European/international prospects?

I mean, how many chances do you get to see that player? Maybe once or twice or if you go to the Nike Hoops Summit. Maybe you see some footage of three of their games but that's really it. Also, some of these players end up staying overseas for a couple more years and then you waste a potential star draft pick. They also seem to be a little less aggressive and softer than some American players. Then you see some players like Pau Gasol and Dirk Nowitzki who have had phenomenal careers so far but there aren't that many elite foreign plays besides those two. I'm not trying to sound like a bigot or something but that's just my opinion.