We can get down the mountain and know that our technique is far from perfect and could be improved, but worry that in an attempt to make us better skiers, we will loose the ability we have gained.
This is a valid fear. New movements require practice to ingrain before they will be as reliable as old movements. There are many who have questioned whether Tiger Woods' repeated swing overhauls have been a smart choice. It's a valid debate. What most people have not seen are the small changes that Tiger has incorporated into his swing in between the major changes. Most pro athletes are continually seeking to improve. They "manage" the severity of the changes they try to make against their schedule so that the learning curve is least risky/disruptive to their performance. If you are not a pro, this level of focus on the sport makes little sense.
While there are many skiers who could benefit from a tear down/rebuild of their technique, there are very few where that is the only useful option. If we can address the fear of regression/learning curve, then the question is whether any instruction is worth the cost to someone who is happy with their skiing. For most people the answer is yes with the right instructor/lesson and probably no with just any instructor/lesson. Without a good idea of what improvements are possible and what those achievements are worth, it's not worth the effort to explore how to achieve those improvements.
In all my years of teaching, I've only told one student that I could not help them and even then I was wrong. She was a fellow instructor who got caught up in one of my video analysis clinics. I taped her skiing on the hill and scheduled an indoor review with her later that day. But when review time came I told her there was nothing I could do because she needed her alignment fixed. When she said "Yeah I know" and indicated she had been putting it off, I detected a lack of motivation. So I do the review session with her anyway. I showed her that she was skiing the best that was possible with the gear she had. I pointed out performance issues that were clearly visible when compared side by side to aligned skiers and in slow motion showed her exactly how the alignment issue caused those problems. Two weeks later, she had her boots fixed and a few days in and was so blown away by the difference that I got my one and only kiss from a "student". Still, I have had many students who skiing did not change after an hour lesson or reverted back the minute the lesson was over.
My point here is that is really hard to see what is possible without professional help. There are plenty of skiers who are on a skill plateau who are also "one small step" way from a significantly improved level of ability. They just can't see what's on the other side of the door. It's a shame to see such easily achieved potential go untapped. But it is understandable. There are also plenty of plateaued skiers who need a lot of work to get to the next level. For many of those, the effort of time and money to get to the next level is not worth it. If you are happy with your skiing, there's no need to worry about what is possible.
But for me, one of the most exciting aspects of the sport is discovering new levels of performance and the opening up of more terrain that this brings. It was easy to think that once I had started skiing double blacks with ease, that there wasn't much value to getting better. But getting better has given me more options on these slopes, let me ski them faster, let me ski them in "unskiable" conditions (e.g. bottomless, solid ice, death cookies, breakable crust) and increased the length of my ski days in ways that I just could not imagine in my days before teaching. One of the unexpected pluses of teaching was finding that "boring, easy" slopes can now be entertaining too. Higher performance = more fun.
I spent 10 years after college exploring the Western US on vacations. I took a few lessons and was disappointed by all of them. I was happy with my skiing and thought that it was cheaper to improve by getting more time on snow (lift tickets) than through lessons (lessons + lift tickets). Looking back I can see the missed opportunities, but it also helps me understand the reasons some people don't desire lessons. I've been there. It takes a certain level of experience, curiosity and determination to break through this phase. For lots of perfectly good reasons some skiers make it and some don't. Life would be boring otherwise. For me, part of the thrill of getting better is sharing what I've learned with other skiers and riders and watching their reactions when they find the other side of the door. Alas, I never get the opportunity to help people who don't knock on the door.