Mandatory helmet laws are not the thing preventing cycling from becoming a viable alternative to cars. Plenty of places without mandatory helmet laws still are dominated by cars, and mandatory helmet laws reduce cycling participation by small percentages - most cyclists wear helmets without being required to, and it's not a particularly heavy burden. I know if given the choice between a car payment and wearing a helmet what I would prefer.

There's resistance to improved cycling infrastructure because there's resistance to improving any infrastructure, no matter how critical, and the overwhelming majority of people don't see a massive rework of the entire transportation system to shift away from cars as a realistic possibility even in the moderate to long term.