Good public transit even benefits those not using it by reducing other kinds of traffic. Everbody should be in favor of such investments but many people just don't think that far during their next traffic jam frustrations in rush hour.

It isn’t that X goes down if you do Y that matters but whether the utility from X going down is commensurate with the cost of doing Y. There is a cost of reducing traffic which I am happy to pay and a cost of reducing traffic which I am not going to pay. So just telling me something will reduce traffic will not induce me to pay. You also need to handle the other side of the sheet.