Robert Fripp is partly to blame for an earlier fall out when he convinced Hall that he could be a serious artist rather than a successful Pop/R&B artist, causing Hall to depart from the duo for a bit. Hall's resulting Fripp-procuced Sacred Songs album, what every artistic merits it may or may not have had (some people like it a lot), sank like a rock on sea of public indifference.
Blame is probably a little harsh. I think they had played out the 'blue eyed soul' part of their career, and needed a break. I was less enamored of their 80's work together, but it's hard to argue with the success they had in that period.
Sacred Songs, according to Fripp, was supposed to be part of a trilogy with
Peter Gabriel II (melt) and
Exposure - Fripp's record from the period, and there are shared songs between them. I never got around to buying Daryl's album, but it if's anything like the other two, it's got to be pretty frickin' amazing. He's got one hell of a voice, too.
Here's one of the 'shared songs' - Mr. Hall certainly shows his prog chops:
Oates, for one reason or another, got the 'short end' of the duo. Not sure of how the writing was split up, but Daryl had the blonde hair, the face and most of the lead vocals. He (Daryl) also been able to purvey his greater visibility into some decent successes outside of the duo, whereas, by choice or whatever John hasn't done that. It might just boil down to levels of extroversion/introversion.
I'd bet (hope) that this all boils down to poor communication. It'd be a shame to have a bad falling out after 50 years as a duo.