In many cases, it's fear.
They're afraid they'll be bad at it, and that they'll be made fun of for being bad at it, so they don't try. This is a society that rips anyone that shows the slightest bit of weakness on a regular basis.
They could also be afraid of what someone (friends, usually) may say if they're interested in something different than what their friends are.
Or they've been told for years and years (at home, mostly) that they're dumb, stupid, useless, good for nothing or worse, so they have zero self esteem. This is VERY prevalent in Title 1 situations.
In some parts of Texas, and in some minority cultures, getting good grades is seen as being "white" and "a sellout" or worse.
It gets worse with gender. For some girls, they're told from birth that their only role on this planet is to be there for a man to make a baby with when he decides he wants one, and so her schooling is unimportant - she'll drop out by the end of 8th grade. In some parts of Latin and South America, it is an extreme exception that girls complete even that much schooling.
Add to that the inherent gender bias against boys in our modern education system - the lack of play, the lack of physical activity, and the forced "sit and get" that is in most classrooms that requires boys to adopt behavior contrary to hormonal desires (kids want to run and play, and boys especially, this is well documented in several studies) and you get boys that are trained from kindergarten to HATE school.
So, you have title 1 students, minorities, minority girls, and many boys that grow up not appreciating our educational paradigm. And we wonder why so many kids struggle in school?
I've had lots of kids who won't learn things even for a grade. To many kids, the desire to do nothing (or unwillingness to put forth any effort) overrides EVERYTHING else, including the desire to get good grades or even pass.
First, SmartMusic was around since the mid-90s (I was an original beta tester). Second, it isn't that band directing has so much as education and accountability has changed. Now, there has to be tons of justification for every point given. That, and kids are different and if it isn't for a grade they (or a large number) won't learn it.
I was discussing grading policies with some band director friends (what else would we do on Corona-break?), and we got to talking about our high school experiences. We were all in high school in the late 90s, early 00s. Several very good high school band programs. None of us could remember any kind of regular tape tests (maybe 1-2 during all-region), chair tests more than 1-2 per year. No SmartMusic - was that even a thing that far back? We did pass-offs during marching season for our section leaders. Everybody got a 97 on their report card unless they skipped a performance - but nobody every skipped a performance.
By the time I went through music school and started teaching, my head director at the time had a comprehensive program of passoffs for marching and concert music. All-Region season included weekly checkpoints on the music (for top band at least). There was a pre-planned curriculum of scales and fundamentals that covered the 3 years of high school band. The biggest part of my job was pulling kids into a practice room one at a time to hear them play their assignments.
I've been through a couple of jobs since then, and every school where I've taught has a system of some sort. Passoffs, recording assignments, SmartMusic, something. Now that I'm the head director myself, I have my own system in place.
Has band directing changed that much in ~20 years?