X-men Issues(9000) then Avengers(4000)??? I thought Avengers began before x-men, should the Avengers have more?

More X-Men series over the years, I guess. Until recent years, there's only ever really been one Avengers series. Also, those both seem like insanely high numbers.

Only recently has Avengers popularity become similar/greater to X-Mens. For decades the X-Men's popularity overshadowed Avengers popularity tenfold. In saying that, there have been multiple X-Men titles for many years whereas Avengers only recently started getting multiple Avenger branded titles. To my knowledge, at the very least.

Because since the 90'ties (or there abouts) have nearly always been 3-5 different X-Men teams who all had a book while the Avengers nearly always stayed at 1 team.

OR in-case you are using CV's appearance counter, there might be a slight multiplication factor due to 1 issue being counted for each reprint in a different language. I am not sure if Avengers are being reprinted as much as X-Men is but perhaps you get the picture when I show you the Top 8 of Wolverine's appearances:

Only half of those of those are in English and the 1st place holder is in Italian (if I remember correctly). Explaining why a 1974 has more appearances than Wonder Woman who's from 1941.

Way more spin offs throughout the years. Avengers have been recently pushing out spin offs.

Pretty much what everyone else said. The X-Men had more spin off titles like "New Mutants," "X-Force," and "X-Factor" than the Avengers did. It was only just recently that the Avengers started getting their own spin off titles like "New Avengers" and "Avengers Arena."