The historic (pre-automotive) main street demanded the highway run through town (so the state would pay to pave Main Street) and later highway design standards for rural highways were fecklessly applied to it, and it's not for decades that highway engineers recognize 'context sensitive design' or 'traffic calming' to make it a street and not a stroad.
A historic main street is wide, because it was full of parked vehicles (even when those vehicles were wagons and buggies) as well as through traffic. So there was plenty of room, even with automobiles, for two lanes of on-street parking and two travel lanes. But the 'capacity uber alles' mentality demanded removing on-street parking in favor of travel lanes, and so you get main streets that are four-lane raceways, in a way deeply deeply incompatible with the existing land use.
Eventually, the existing land use shifts, as every other building is knocked down for a parking lot with a curb cut, or demolished and replaced with something where half the lot square footage is parking lot.