Lots of reasons. The training is quite condensed, and the initial academics are taught by people with no experience or context. And then if a student self-identifies as being behind, the training department knee-jerk reaction is to label the student a whiner and tell them to suck it up and fail like a man, regardless of how much experience that student has.

I ran a major flying training shop for a couple of years, and our instructor training shop for a year. Among other roles, I was responsible for identifying students who were at risk of washing out and making direct recommendations to the boss on if we were going to keep them or wash them out. So I have some experience judging when a student is at risk of failing. Asking for a single study day to prevent failing my checkride got me the standard spirit training answer of "All students complain about the program, suck it up, request denied."

So it's a combination of a minimalist training program, inexperienced instructors, and a training department that is at least partially stuck on stupid. My advice to anyone going through spirit training is to quit early if you think you're gonna fail, since there's absolutely no reason to ever go to a checkride you think you might fail. Call out sick, chop off a toe, whatever it takes, but do NOT go to a checkride you're not fully confident you'll pass. And certainly don't fail a checkride for $38/hour and a restraining order. You're much better off explaining why you quit a training program, than having to explain a checkride bust or getting fired.