A few things work against private pilots checking notams:
1) pilot age distribution (many never got to grips with basic IT)
2) historically crap PPL training in this area of the syllabus (NO notams taught where I was in 2000/2001)
3) lack of internet access (or publicly accessible internet access) in many places that people fly from
4) "flying should be like our fathers did it" attitude
I'd say all the above are equally widespread.
Since most new PPLs drop out fast, most of the long-term crowd has been flying for years, and these people will not be hanging about within any school/club environment. So, the only opportunity for education is the 2-yearly flight with an instructor, but the syllabus for this flight doesn't cover internet usage
Also, most people who don't want to get into new knowledge areas will choose an instructor who they know is not going to cause them trouble. Certainly, that's what I would do.
The present internet notam system has been about for only about 6-7 years (in a usable form) which is far less than most old-timers have been flying.
The comprehensive solution - a laptop with mobile internet access - is far too esoteric for the vast majority of pilots.