The Worst PROG ALBUM

These are not prog rock albums

Genesis - We Can't Dance

Rush - Vapor Trials

Both artists lost their prog rock status by the 80's.  Why do you think Steve Hackett left Genesis; and Rush gave up prog rock when they left Mercury Records.

I can't really comment on Tres Lunas, Rock Island, or Vapor Trails since I've never heard those three.  Other than Love Beach and possibly Deseo, none of these albums are bad enough to cause me to vault in front of a moving train.  All of them could arguably be considered only prog-like, or just flat out pop (We Can't Dance), which is probably why you have them listed on a poll of worst prog, not necessarily worst album ever (which would be a really fun poll to read in itself).  I wonder what kind of responses you'd get to the question, "What is the most disappointing prog album you've ever heard?".  I can think of a few:

Asia (first). Loved it actually, but very underrealized potential considering the all-star lineup
Drastic Measures (Kansas). Anyone who's read more than 2 of my threads knows I love these guys, but this one was a complete turd.  No violin, no Steve Walsh, chessy compositions from John Elephante and his friend Yanni (not really, but it sounded like that).  The album title speaks for itself.
Lisztomania (Rick Wakeman).  I'm not a huge fan of Wakeman's solo stuff anyway (I like most of it, it's just the context is usually too European so some of the lyrics go right past me).  This one though is one of the few things I've heard that could have caused me to start drinking again. What a depressing piece of crap!  Somebody should have given him a hug in the studio.
Remixes (Yes).  Some were remixed so much that they weren't even recognizable anymore.  I read somewhere that some of the band had their kids, dogs, neighbors, and bookies helping out with the project.  It shows.

We are missing two Yes albums - Union and The Ladder. For me they bring more disappointment than Big Generator (or Pig Generator as my friend says), for which I voted.