Not sure the bcd is the same. Also historically the spiders on road bikes were five armed and mtb four armed. Not sure why one should be easier to set up than the other.
A somewhat short term view of "historically"
MTB Triples are (or were originally, when mountain bikes first became mainstream) 110/74 bcd 5-arm, with a smallest middle ring of 34T and a smallest inner of 24T. 110/74 triples are still popular for touring bikes and hybrids.
Road Triples are 135 or 130/74 bcd, so the smallest middle ring is 39/38T - i.e a standard road double with a granny ring. (135 is Campag)
5-arm MTB triples then evolved, in the name of weight saving, into Microdrive (Suntour) and Compact Drive (Shimano) with 5-arm 96/56 bcd (or thereabouts, the two were different). These often came as 20/30/40T chainsets.
Then 4-arm MTB chainsets arrived, with a slightly larger bcd, so the smallest inner was 22T.
At about the same time, the original MTB triple lost its 74 mm bcd bolts and became the compact double, on road bikes for ordinary folk who weren't as strong on the hills as the pros.
It's mostly fashion, and marketing advantage over the other chap (the attempted component lock in is only ever short term).