In May of next year, [The Avengers: Age Of Ultron](movie:293035) will be released and tons and tons of people are dying to go see it. (Myself included) So far, the Avengers line up for the movie is Iron Man, Thor, Captain America, Hulk, Black Widow, Hawkeye, Quicksilver (Not the one in X-Men DOFP) and Scarlet Witch. Right now, the team has eight members, not including Fury, Hill and Coulson. That is an extremely small number compared to the number of Avengers in the comics. In the comics, there has been 143 different members. Some of them have been around since 1963 such as Ant-Man, Thor, Iron Man, Wasp and the Hulk, while on the other hand some of them just joined last year in 2013 such as Hyperion, Ex Nihilo, and Manifold. In that 50 year time span, many heroes have joined and left the team.
Many other heroes from other teams have been Avengers such as Wolverine, Beast, Storm, Mr. Fantastic, Invisible Woman and The Thing. For the full list of all of the Avengers click here. I feel like there are too many Avengers. The Avengers are Earth's Mightiest Heroes, since there are so many Avengers not all of them can be the Mightiest, so here is why I think Marvel added so many Avengers.
I think Marvel put all of these superheroes in one team because it introduces readers to new heroes and creates more publicity for less known heroes. For example, if you are a X-Men fan and you read most of the comics, obviously you would read anything X-Men. Well, if you find out that The Wolverine, Storm, Beast and a few more X-Men are Avengers, then you would read Avengers comics. Marvel added smaller superheroes that aren't as well known and put them in the Avengers line-up, then more people would read about them and their independent comics would become more popular. For Pete's Sake!, who knows of Blue Marvel and Whizzer, well they were both Avengers at one point. The Whizzer is basically the non-mutant version of Quicksilver. This is also good if readers want to find some cool new characters, but it also be a little bit overkill.