x men cinematic universe - Why is the production team making prequels of X-Men rather than sequels?

I am a die-hard fan of the X-Men animated series X-Men Evolution and I also like the X-Men Movie Trilogy

In addition to the main trilogy there are two more movies (X-Men Origins: Wolverine and X-Men: First Class) which are prequels.

Why have the writers and directors decided to do prequels rather than a sequel?

Wikipedia says that they are planing for a sequel for the X-Men First Class movie but there is no clarification about an X-Men 4 movie.

Answer

I think this quote on the X-men: First Class wiki page gives us a decent amount of insight as to why they're making "prequels":

As producer Simon Kinberg read the comic series X-Men: First Class, he
suggested studio 20th Century Fox to adapt it. Kinberg, however, did
not want to follow the comic too much, as he felt "it was not fresh
enough in terms of storytelling", considering them too similar to John
Hughes movies, and also that the producers wanted an adaptation that
would introduce new characters. Both Kinberg and Shuler Donner said
they wanted characters with visuals and powers that had not been seen
yet, and that worked well as an ensemble even if they did not work
together in the comics.[11] Shuler Donner later said the original idea
was to green-light First Class depending on the success of X-Men
Origins: Magneto

So we see that they wanted a shift in focus from the main set of characters established in the X-Men trilogy. While quite a few characters were introduced, the main plots revolved around only a hand full of characters.

Another reasoning is that the X-Men universe is quite vast and dynamic. Each character has more than one story arc that just can't be covered in one or two movies. For example, if we look at the story arcs for Wolverine, we get something like this:

• Pre-Memory loss (X-Men Origins: Wolverine)


• Post Memory Loss (X-Men Origins: Wolverine 2)


• Wolverine and the X-Men (X-Men 1-3)

Also, character story arcs criss-cross in the X-Men universe. It is literally a giant bowl of spaghetti, complicated even more by time travel in some instances.