I’d just assumed it was the natural low brass aptitude in handling containers of alcohol. 
Me, I used to be a cellist – put a wheel on that endpin, and I’m good to go…
It’s not pretty. Most are made specifically for outdoor cold-weather marching, and as long as they are roughly the same size & shape as a “real” mouthpiece, they’re considered fine. I’ve never lived anywhere cold enough to warrant buying one, so my experience with them is mercifully limited.
Slightly off-topic, I have seen a plastic mouthpiece that was designed for a specific sound improvement. It had an aluminium shank, and the cup and rim were formed from a thin sheet of clear plastic of some sort.
Trying to describe it…picture a clear plastic cone-shaped funnel, with the edge at the wide end folded inward to form a flat rim. Now tuck that edge under just a bit more so that it doesn’t cut lips, and that’s pretty much what it looked like. The effect of this is that the cup has a greater diameter than the inner edge of the rim.
The idea was to facilitate low, loud playing by not having cup walls for the player’s lips to slap into - this is apparently a contributing factor to tone break-up and general nastiness at extreme volume. It also looked freaky 'cause you could see the player’s lips as he played…
To some extent, it worked. Tone actually seemed fine, and the low register was, ah, impressive. 
I’d have loved to keep the damned thing in my pocket, Uke. The foolish uniforms we wore had no pockets. Or even a slit to allow access to your pant pockets.
Ah, I see. Uniforms, eh?
At Andover and Princeton, don’t chew know, we wore dark blazers and gray flannels, with straw boaters and a silk paisley ascot.
Suddenly our uniforms, despite general ugliness and a careful design intended to keep the wearer warm in summer and cool in winter, don’t sound so bad.
We didn’t have pockets to start with, but most of us either added them ourselves or prevailed upon sewing-competent relatives to do so for us. The minimalists settled for side slits in the pants to allow us to reach inside pockets. It was rarely cold enough in Louisiana to require prewarming your mouthpiece, but it was more comfortable.
And at Rice, we wore zoot suits, fedoras, and sunglasses.
Hyuk, hyuk, hyuk.
This reminds me of a zany movie I once saw on video, titled Outtakes. A small classical combo with three men, one the conductor, and three women: a pianist, a saxophonist, and a cellist. As the music played, getting more and more lively, the saxophonist–who had been playing “Deep Throat” with the mouthpiece end of her instrument-- suddenly yanked her blouse off–and she had no brassiere on! The cellist–who had her knees around the cello with its back very close to her loins–got her blouse torn off by a man whose trombone’s spit-valve snagged the blouse. (The pianist kept all her clothing on.)