Why did this never get a sequel?

It actually didn't perform as well as Fox would have liked. A film with this budget generally needs to see a number in the high $300 millions at the box office to get a sequel. Think the Star Trek reboot with its $386 million or "Batman Begins" with its $374 million, both of which had comparable budgets to FC. Granted, it's a little more complicated than that when you factor in the difference between domestic versus foreign earnings but, nevertheless, at $354 million, FC would have struggled to break even.

It made $146,408,305 domestically, of which Fox gets about half (it splits that money with the theaters). Their cut of the additional $207,215,819 from foreign theaters is significantly less as countries institute tariffs designed to keep too much money from leaving their countries. Those vary from country to country, studio to studio, (the bigger studios tend to be able to work out better deals than the smaller ones since they do more business) and even film to film. Let's be generous though and put Fox's overall take of that at 35%. Adding in the 50% of the domestic take and Fox may have actually seen around $145 million from box office earnings.

FC has an estimated budget between $140-$160. Let's say it's not on the higher end of the scale and that above figure covered the production budget. Now you have to factor in advertising. We rarely get those numbers but for a film like this they probably spent around $80-100 million so that's how much they need to make up in after market revenue. We do know that its total domestic video sales are around $67 million, which sounds great but take out production costs, the retailer cut, and more advertising money spent and that number declines.

You then have things like foreign video and TV rights. I don't have numbers for those, but they're not going to be stellar. So, you're looking at a movie which may not have broken even (at the time when they were deciding how to move forward, that is). Combine that with fears that a sequel will lead to diminishing returns instead of doing better and if it wasn't for this idea to use the original cast to promote the new cast a movie like this would normally not get any kind of sequel.

This is an near-perfect X-men movie. I know what you mean zombie.

probably because bryan singer is there guaranteed cash cow director so they pretty much a ok everything he wants to do with the x-men sides imo first class probably was the worst of the franchise. none of those mutants on magnetos team was all that interesting.

Matthew Vaughn was originally going to direct DOFP too, but backed out due to creative differences. I imagine his version would have been closer to a direct sequel, but hard to say.
https://www.youtube.com/watch?v=mZuqdaO0Sgg

First Class was a relatively interesting and refreshing take on the X-Men franchise. And a "real" sequel that focused on Magneto's team, as well as showing us the beginning of Xavier's school - up to the time the war started - would have been neat to see.

That said, I don't see it as necessary. I'm content with Days of Future Past, and ‘far as I’m concerned they went in the right direction.

Yes, I wanted to see more early 1960s X-Men. Instead, we jumped forward to the 1970s, an era that I can't stand. Thankfully, DOFP was an excellent movie.

i wish they did make a sequel. a direct sequel.