I'm sort of confused why mountain bikes went 1x first before road bikes.

The gear range needed for MTB's (and touring bikes and hybrids) is very wide and thus favors triples, even if they're finicky. 3x9 systems have, effectively, 13 well-spaced ratios. You hang out in the middle ring most of the time and if you need to go to the high or low range it's a nice double shift. The 2x systems by comparison have a huge awkward 4-step jump between the big and small ring, and they are often cross chained, because the middle ring is missing. I suppose the idea is to hang out in the top ring til you really need the granny. The 1x11 systems don't cover the range so they just outright sacrifice two or three ratios - whether on top or bottom depending on your chainring choice.

By comparison on the road, a single 44 ring with an 11-N cassette compares very favorably to a 2x7 system, and beats the snot out of a 2x5 system.