Destinations drive demand, not traffic lanes. A road can be so inadequate that the traffic makes it painful enough that might I decide to just stay home when I'd rather go somewhere, but the demand is obviously there either way. Infrastructure should enable us to do the things we want and get to the places we want to be.

I don't understand how people view making or keeping streets so shitty that many people can't or won't use them to get to where they want to go as a good thing.

Widening the road doesn't necessarily create demand (although it may, by making a given route more attractive to folks who would otherwise have worked/shopped/traveled elsewhere), but it does shift demand away from mass transit and towards individual vehicles.