Cessna's JPAT proposal was a lot different then the Tweet: http://jetav.com/the-citationjet-that-wasnt/
It was designed with extremely easy maintenance in mind. A lot of things would take longer to fill out all the paper then the actual work.
You do make an excellent point about the advantage of side by side for a primary trainer.
If JPATS is so easy to maintain, why are there about 3000 "urgent" change requests dating back over 10 years that have not been accomplished? Seriously, that plane is a maintenance nightmare only because HBC has been unable/unwilling to fix even stupidly simple problems with the plane and the USAF isn't holding their feet to the fire. 3000 or more major maintenance changes, some of which could result in the loss of the aircraft or major damage, going un-fixed for a decade.
Sorry, JPATS was a huge song and dance. It works because a massive effort was made to sell the USAF a complete training SYSTEM (including sims, academics, etc) instead of just an aircraft, but that also means that the program was sold on the bottom line - cost efficiency. And that means that we got what we paid for, and we apparently didn't pay for HBC to do little things like wrap wire bundles so they don't chafe, and when we discover a chafed wire bundle in 90% of the fleet and have a really easy maintenance fix, the fix goes 10 YEARS without being implemented, resulting in thousands of man hours lost inspecting and taping that damned wire bundle up over and over. Multiply that by 3000 similar problems and proposed yet un-implemented fixes, and that's what the easy to maintain JPATS looks like to a maintenance supervisor. Yea some things are easy, but the plane is still a jigsaw puzzle with thousands tiny stupid problems that could be fixed, but aren't.
I'll give you another example, that caused me to recall an aircraft. A function check found a bad fuel shutoff valve, but otherwise the plane passed the functional check. Maintenance replaced the valve, which required an engine run. The engine run tech order doesn't include a test of the replaced fuel shutoff valve, nor does it trigger another functional check. So they ran the motor, did not test the valve, and put the plane back onto the schedule.

I had to recall the aircraft, logged the sortie as an air abort for maintenance, and of course maintenance blamed it on HBC and the USAF for leaving such an obvious glaring loophole in the maintenance procedures. They should have been smart and called our FCF pilot to test that valve before it got on the schedule, but the tech order and maintenance cards should have covered that item. That was 4 years ago, and I would bet $20 that the manuals have not been updated yet in spite of this being a potential cause for an uncontrollable inflight fire if that valve fails to function when needed because it wasn't properly tested.
Multiply that problem by 3000 backlogged change requests dating back to the beginning of the JPATS program...
Some people wonder why I'm not such a fanboi of the AT-6 program. I'm sure it would be a fine aircraft especially for an air force using the T-6 already (like the Iraqi AF), since the basic transition training would be a really simple aircraft checkout, but I've seen HBC's game. The HBC employees I've worked with directly have been great but the overall program management has left me with a lot of questions about why some parts of the program are run the way they are run. The more I learned, the more I paid attention to teeny tiny details during my preflight and postflight inspections.