Not optimal? Really? If a monorail is allowed to deteriorate to the point it is in such poor condition, exactly how awful would it have to look to actually describe it as 'bad'?
Even one sick fish in the ocean is unacceptable if you are the poor guest who is served that particular fish over at The Boathouse. Similarly, even one hotel room - or one monorail coach - in run down condition isn't acceptable; Some guests, paying the same as everybody else, are going to receive the lesser experience. If you were staying at the Grand Floridian for $600 a night, would it be "not optimal" if your room was dirty with stained bedding, torn and broken furniture, and dingy walls or would you be livid? Remember, all the other rooms in the hotel are just fine.
That explains how the trains are allowed to run in such poor condition, but not why. That responsibility lies solely at the feet of Disney management. You may need more custodial personnel or more mechaincal attention, and probably increased budgets, but point is the trains are only in such abysmal condition because it has been allowed to happen. It doesn't have to be that way, and rather than making excuses for it (true though they may be), we should be highlighting the true source of the problem. I completely understand what you are saying, but again, that's not the real issue.
There are passenger train cars operating tonight in this nation which are nearly seventy years old; Some of them will be on the road for 48 hours straight (or more), be serviced in 12-18 hours or so, then do it all over again week after week. They don't look like this. Monorails, however, can visit the shop every night.