Often in old European cities there is no space to take away from, unless you cut from pedestrian side, or rebuild whole block to have wider gap. Or you completely remove that single one way lane, and good bye resupplies for the shops/restaurants and good luck to those poor folks that will move in/away. The bigger the city, usually the older it is, and center looks like this - tons of single lane one-ways.

US roads always stroke me as super wide and at least those I saw myself had plenty of space for this.

One example to illustrate the difference - on say Swiss or French car parks, if you park perfectly in the center of the parking spot and if cars around you do the same, even with regular car (say BMW 3 series) you can't just open the door fully, often not even that half-open position in the middle. Significantly wider cars effectively take 2 spaces, but then again not many folks buy them here also for this reason.