For urban areas where it could potentially work, corruption; classism; NIMBY; poor education about taxes, their uses, and their benefits; and selfishness.
For inter-city, some of the above but also getting the property on which to do it seems to be a huge pain in the ass when looking at projects in Cali or proposals for others such as Texas.
In most of the capitalist world, transit is getting increasingly defunded and low quality, except high speed rail in some countries (which idk if counts as transit)
Less than we used to and in most places not working that well. Denmark cancelled nearly all train projects when the new government took power and greenlit a bunch of highway lane expansions instead, which are far more expensive.
One thing not said is that you don't really have a politician who gets fired directly for bad mass transit. Most mass transit has to function outside of the main urban city and commonly has to go beyond other counties. So you either get a multi county organization that isn't directly accountable to the public or the state that creates interference from rural voters who don't care.
One problem, at least in my area, is that to do anything but use busses requires coordination between multiple local governments and often county governments. Aside from the eminent domain, just planning between these groups is cost prohibitive.
There's been a few light rail projects that would work well on paper and really ease congestion, but because there are so many little fiefdoms they've never gotten off the ground.
We don't have people who can design high power inverters and controllers, motors and other such power handling devices required to build the propulsion systems.