I learned TIG on my own through trial and error and youtube videos. If I only had tig, I would have hated building anything when starting out. Welding is half the battle. Fit-up is the other.TIG definitely is harder to perfect, but in this day and age with a plethora of videos available online, it's not the "hands-on instruction required" process it used to be. I've coached quite a few people on open root pipe welding just through messaging, and watching thorough close-up videos are even better than that. I don't know if you've seen my other posts, but I'm a specialty code welder by trade. I was picked up to be a welding instructor, but turned down the job. I feel pretty confident that I can teach most people you TIG just through talking and referencing some good videos.
The other aspect is that you can tell if a TIG weld isn't sound just by looking at it. Even if its a little ugly, you can see if it's fused. The same can't be said for MIG, and when you are throwing in the beginner DIY factor with road-going vehicles, it's not really recommended. But people are going to want to try anyway.
And for the welds that are too dirty for TIG, every TIG welder is also a stick welder.