Alan is bigger in his own mind than real life. He talks earnestly about working with big artists but none of those doors would have opened without mk. There's a hint of this in everything he says publicly about DS....
Alan joined DS because he is an amazing player.
His contribution on MK's music was huge.
His inputs thru the songs are amazing.
I think that, on Dire Straits, his inputs are on level of brilhantism Mark's guitars.
Even GF said that the recording of Local Hero soundtrack (the best from MK) was based on Mark/Alan extensive experimentation.
Not MK, not Alan, but both.
Everyone needs a first platform. DS was/is the first step for him to play with Eric, Dylan, Harrison, Bee Gees, Tina...
OK, most of them happened because MK.
Don't forget. MK is an artist/composer, Alan is a keyboard player.
Mark is a genius, Alan brought his insane musicallity to MK's music sounded better as they can. So, his work with Mark opened doors for him to work with other people.
I believe that he was tired to be on A Game and gave to himself a calm life.