Right, if safety is the reason, then how can it be safe during the daytime?
Perhaps it's truly not

.
(This was just the most recent quote on the matter, many others have said the same thing).
As for the train numbers thing. I don't see 8-10 of 10/11 "a fraction of" the available trains. They typically run a base of 8 as we see earlier and increase to 10-11 on the super busy days (or even just as peak times come up). While 8/11 is technically and mathematically a fraction, that's not where you use the term "a fraction of". So, we possibly have "a fraction of" the trains left in the barn for the day, and those can get maintained just fine. The others, not so much.
However, that's neither here nor there, it's just interesting to see someone so adamant that it's all about one side, be so considerably off of what he uses to base a portion of his position.
--
The real reason is likely "All of the above". Train/Track work, train/track preservation (reduced wear and tear), along with cutting costs down a bit. It's very unlikely that this decision was made solely for a single factor.
The timing, is likely either moved up due to recent issues with the track (I'd guess they've had this plan in place for awhile, just were waiting until slower seasons to launch it) or because they actually know the difference in usage between the summer (when the only post closing time is EMH) and the fall (when the parties take up several nights a week along with EMH). Starting this at this time of the year can test the system and work out transportation kinks that would threaten to blow up the whole system come fall.
The same deal with doing Epcot ahead of MK. The Epcot line is quite a bit newer and less heavily traveled than the MK lines (surprised no one mentioned that

) and the demand for monorails post regular close is likely a lot lower since you only have the Poly/GF/CR resort guests and a handful that may have parked at TTC that day. (Compared to the same resort guests (minus a few that walk to CR), plus everyone who drove to MK).
I'm sure it's a mess right now, I'm sure that it'll get smoother after awhile. I'm sure it'll become a mess again once the parties start rolling around, and I'm sure that it'll smooth out again.
(As a note, I'm staying pretty neutral on the actual matter here. Only trying to provide a different perspective).
(Edit: As far as the bus to CR goes, while I don't know and no one has mentioned it here, I'd venture to guess that they'd have to have one, specifically for guests with mobility issues. Whether or not that's open to the GP is another story, but for those with mobility concerns, I'd strongly guess that there is one. Maybe someone who's been there since Monday and has asked that specific question can clarify).