I've found several accomplished turners who use the Minwax and other off-the-shelf finishes and it appears they get great results. On the other hand, there are a lot of accomplished turners who say they wouldn't touch Minwax if you paid them.
Is this a case of snobbism (?), preference for using traditional methods, or is it difficult to work with and get consistent results?
It's the usual business of hating the "big" guy. If you look at the tests in most magazines, there's not a lot of difference. One of my favorites, Wipe in/on Poly by Minwax, was rated the best in class a few years back. Goes without saying that conspiracy theorists count advertising inches in the magazine as rebuttal.
Probably not an awful lot of ways to mix solvent, resin and oil to distinguish it from other products, other than varying the ratio of actual finish to pollutant. Consistency in product leads to consistency in result, so if you like what a product does for you, use it. If it happens to be a Minwax product, cover the label....
-------------------- Better to follow the leader than the pack. Less to step in.