A think it must be a local thing, I dont really know anyone worried about 50".
It is a local thing and there are a LOT of 50 inch gates on B.L.M. and National Forest ground throughout western Colorado.
The ones I know of are in areas with trails along ledges where a wider machine will not fit. Then having two machines head on, without being able to turn one around is tough.
There is still a lot of area to ride outside these gates in western Colorado, so there are a lot of wide machines sold.
For your thought about being worried about one of these gates, that can be a big problem.
The worst problem for finding one of these for the first time is running out of gas.
I know of a couple gates that are well out on the trail from the trail head I use. If you use a map and plan a long looping day ride and can't get through, backtracking or going around without running out of gas can become the problem.
Another way these 50" gates cause problems is finding one late in the day. Running out of light while backtracking can be a big problem. I have ran onto others lost because the trail looks different going the other way. I have had a few times I ran to the truck for a gas can to help someone stuck on the trail.