LOGAN DOES.
Yeah.
"Life goes by pretty fast. If you don't stop to look around once in a while, you could miss it."

yay I might be on the right track..
I was born on this ship. The world passed me by, but two thousand people at a time.

Yes I'm aware that some Alzheimer patients are plagued with restlessness, anxiety, and violent outbursts. That's definitely not happening here.
So save the theories for MatPat.
Benjamin Franklin once said: "By failing to prepare, you are preparing to fail."

I think Charles either accidentally or intentionally wiped the X-Men's memories clean and gave them new lives. I think it was an intentional act though.
See the Reavers, at least in the comics, were totally set on killing all of the X-Men, and were on the verge of doing it too. The only escape for the X-Men were to scatter to the four corners of the Earth and start new lives, and they unintentionally got their memories wiped in the process and couldn't remember their time as X-Men.
I think something similar has happened here, but the process didn't work on Wolverine because of his fast healing superpower (he didn't lose his memories in the comics either, and was the last of the X-Men left), and it didn't quite work on Charles Xavier either because he did it to himself and somewhere in his mind he knows what he did, it just scrambled his brains somewhat.

This makes most sense

I hope they didn't all die at once. I remember reading a comic as a kid (apparently it was an alternate universe, but idk) where Wolverine and Storm were the only two X-Men left after the rest were slowly hunted down by Sentinels.
I like that idea, even though the Sentinel program was dismantled in DoFP. If all the mutants were taken out by one event, that would feel sort of lame (to me).

My guess is that Mr. Sinister has been using the Reavers and Caliban to hunt them down. Only reason Logan is spared is because he already harvested his abilities.

This takes place some time in the future. In one of the Wolverine comics, I forget which one, you see Logan looking older and remembers back to when a mutant controlled his mind and he killed all the X-Men thinking they were bad mutants. This movie might be following that story.
I used to do drugs. I still do, but I used to, too.

I dont think they're dead, whats the point in making more movies if they are all dead?
They may be trapped in another dimension or something like that

Come to think of it
*Prof X is supposed to be suffering from dementia or Alzheimer with the most powerful mind in the world, any thing can happen and could even tap into the disease's possible violent nature.
*Is Logan hiding the Professor or is he keeping the Professor away from doing more devastation?
Hmmm.

Hmm, Professor X sounds more plausible.
Whatever you are, be a good one.

I heard a similar theory that Wolverine killed them all under mind control from someone else

Yes it was, he was being used to first kill all mutants and then kill all humans. But that was hooked up to Cerebro not his normal power.

So yeah, that's how I feel anyways

Wait, wasn't this a plot point in X2? Perhaps someone used Cerebro against him?
Whatever you are, be a good one.

That would be pretty dark
Some BODY once told me.

Plausible theoryor
have you seen any early screening