Let's say you're an 18 year old new CM. You've worked at McDonald's for two years, and you've never experienced the type of "stellar customer service" people expect at Disney. Unless someone - say, a lead or a training course instructor - impresses upon you that the expectations are higher, you won't necessarily get it. If you go in with the idea that it's like your McDonald's job there's no hope that you will raise the bar.
When I was in customer service, we had seminars that went over everything from the types of greetings we should give to the words we shouldn't use (example: at the time, terminology was changing and we were admonished against using the word "handicapped.") to the specific ways we should and shouldn't address disabled guests. The fact that the company emphasized it meant that we saw it as more important.
If Disney took the time and energy to reinforce pleasant customer service skills with their CMs, the quality WOULD go up. Right now, they aren't taught to see it as anything of great importance.
Over the decades, the books, college papers and corporate seminars that have discussed, analyzed and imitated Van France's innovative "University of Disneyland" are legion.
Sadly, the world-famous training philosophies and procedures he developed in Disneyland's first decade have largely been tossed & trashed by the Eisger regime.
At DL, people are paying hundreds, if not thousands, to have a fun vacation. The focus of the CMs should not be efficiency at DL (like it is at CVS, although of course incompetent CMs who take forever are also inexcusable), it should be customer service.
The example about one CM doing two or three CMs jobs and not being able to provide ample service--that's a terrible example. At CVS, sure I'd buy that, but at Disneyland, if you have to do more work than you should, your focus should still be on the guests, not on getting as much work done as possible. It used to be that, while getting the job done was obviously important, catering to the guests and keeping them happy was of the utmost importance. Say a cart stocker has to drop off ice cream to the nearest cart because they're completely out--you're arguing that it's ok for them to blow everyone off because they have a job to do. However, in a proper service environment, the CM would first take care of the guests should they need anything and be polite.
From my own experiences growing up around the parks (worked for Knott's at one point, had/have several friends working for The Mouse currently), they're just not offering enough money.
The demands on CMs are higher than any other job of equivalent pay locally. You can go get a job stocking at Target starting at the same as Disney or higher, and not have the "on call" status where future hours get docked for inability to show up on short notice bonus shifts. Where extra time caused by the company is paid for, not included in your "you should expect it take take three hours to get from the company parking lot to work" lecture.
Disneyland used to be a gold standard startup job in OC. You knew you were going to get paid better than your other friends who weren't working there, you knew that the standards were high and likely were bragging that you met them when you talk to your friends from Knott's, you had a job that felt worth keeping. Then the last twenty years hit, and that's pretty much In-and-Out Burger now.
Disney is no longer willing to pay a premium rate for employees. Instead, they offer rock bottom wages and less than perfect working conditions in fairly stressful environments.
With that comes what you should expect from dredging the bottom of the barrel. Workers with a developed sense of responsibility are not going to be willing to stay at an entry-level minimum wage job with little chance of advancement when any other option pays more. For years I've been reading complaints here about/from TDA about the lower amount of applicants and the lowered standards that they now face on hiring days, and that's something else that is directly traceable to the low wages.
You can't expect high-caliber performance from low-caliber jobs. At least not without severe disappointment.
So yeah, there's a good chunk that could be solved be CMs being nicer etc., but there's no real incentive to. What is the worst that is going to happen? Unless you're a fan, getting fired by Disney means you're free to go pursue some other dead end minimum wage job that is likely to be easier and treat you better.