I looove my nylon bridle! I don't have to worry about it getting dirty, wet or muddy. I can swim with it and it can sit outside in the rain and I don't have to worry about it getting moldy. I can not stand people who judge me because of it.
You covered low maintenance and durable, but left out light weight. It's not just bridles (and I ride with non leather halters anyway). When I'm ready to ride out for long distances I replace my stirrup straps and cinch straps to nylon (if they're not already being used). The saddle is the only thing I haven't yet been able able to bring myself to go synthetic with, but my next one will have 1/3 less leather, because leather weighs so much and I don't need flaps or fenders. The only reason I'll use all leather is when I'm working on load bearing and I want the weight then.
As I pointed out to a camping buddy (he doesn't ride) who asked me why I replaced leather straps on my saddles with nylon? He loves leather and we both wear leather jackets, coats and hats. I asked him if he'd rather trade in his synthetic backpack for a leather one, possibley have a tent made of leather, etc... and why didn't he wear his leather coat when we went camping?
Of course his answer came down to weight and mainenance. Which is what I pointed out with the horses. If he were a horse would he rather carry around those extra lbs of leather or have the weight reduced? The light bulb in his head finally turned on
. Of course then I had to explain why I used a saddle and didn't ride bare back
(same reason he uses a frame with his back pack).