I suspect a big reason guys who do their own tire changes don't use Ruglyde (or some other tire specific lubricant) is that they don't know about it. If your source of "how to" info is something like Uncle Joe the backyard mechanic, or Youtube, or motorcycle forums, you see and read about a lot of guys using everything from dish soap to Windex to WD-40 (??), but very few ever seem to advocate an actual tire lube. I first learned of it about a decade ago when Greywolf talked about how dish detergent could be corrosive to rims, and was a poor choice. I had immense respect for his motorcycle knowledge, so Ruglyde is what I began using. I've tried other things like dish soap and Windex (though never WD-40!) before I was aware of Ruglyde, and Ruglyde just works better.
I can envision a person who's just starting out with his own tire changing, looking at a gallon of lubricant and saying "man, I'm never gonna use all that, and I have Windex under the sink, and ScreamingBiker69 on Youtube said it was perfectly ok to use", so that's what they go with.
A good rule of thumb for changing motorcycle tires by hand, using hand tools, is "if you can't get the tire on, you're doing it wrong".