Hmm... well... for me personally I love Pokemon so much because I have lots of nice memories at the times years ago. Besides I like it since I've been a little kid and I can't stop loving it suddenly o_o
Otherwise, the games won't get boring after playing them a long time and the fact of collecting Pokemon, to train them and battle with them makes people addicted to it.
That's why Pokemon still exist after more than 10 years, I think.