Cowboy Shirts Are Just What Cowboys Wear
“Cowboy” this or “Cowboy” that almost implies some sort of uniform that cowboys are required to wear. If you haven’t noticed, cowboys have a tendency to be somewhat independently minded. Telling most cowboys they have to wear or do something specific probably isn’t going to get the results you wanted.
However, go to a rodeo or western dance, and you’ll probably see a lot of very similar shirts. You can probably take it to the bank that is the result of the wearers not being told they had to wear them, but chose to anyway. You can also take it to the bank those shirts are “Cowboy Shirts“.