Why are there few level 3 and 4 instructors out there? In Canada? Dunno.
TLDR: Our terrain isn't great and it's too far away, and that makes it far more challenging to improve.
For me, all the factors I mentioned earlier are hard to bring together in Ontario. The nearest OK hill is 1.5h away from Toronto, the largest population centre, though my main coach hates skiing there. The hill where level 3 exams run is 2-2.5h away. And even at that, neither hill has a
lot of terrain that helps you discover or consolidate the sensations of good skiing.
Skiing is a real sensory sport. When you find the "sweet spot" on your ski, turning becomes far less work. When you feel yourself balance on the outside leg at the top of the turn, it gives you the ability to shape the turn. When you allow separation to occur between the upper and lower body, your legs "unwind" into the next turn all on their own. These kinds of outcomes give you physical "feelings" in your body. Once you've locked in a feeling, it becomes your reference point. If the next time you ski, that "feeling" is gone, you can run through your checklist and self-assess and self-correct. E.g. when I'm not feeling good steering or can't easily initiate a short radius, for me, I revisit my separation and my mobility, and 9 times out of 10, I can get that feeling back. But I can only self-correct because I experienced those good feelings in the first place.
In Ontario, and probably in many parts of the US, our terrain is almost all too easy or too short to
easily develop good feelings of high performance skiing. We have one bump run about 300' in length, or a genuinely steep pitch that also flattens out after about 300'. Any intermediate skier can skitter down those two runs and think "wow, I did it!". But a developing skier needs more time to carry the good feelings from easy to hard terrain - and that's tough to do with such a small amount of good terrain.
Somewhere like Mont-Sainte-Anne, in contrast, has genuinely long stretches of steeps (e.g. Super S) or bumps (la Soumande). These stretches let you either "lock in" a good feeling, or coach you that you don't have the feeling--and allow you to sort things out on that same run. I have (re)discovered more good feelings at Mont-Sainte-Anne in my first 3 days of skiing here (under level 4 coaching) than I did in the multiple months spent back in Ontario.
So while it's possible to become a level 3 or 4 skiing mostly back home... it's felt like an uphill battle, even with the awesome coaches we have available. Hats off to the folks who can pull it off. Back on topic for the OP, it would definitely help to move closer to awesome skiing! But even if you can't do that, a good multi-week stint in a training program like Rookie Academy would help you get close to your goals (save those pennies).