Should roads be free? The evidence, from a 50+ year experiment is no. Free roads leads to overuse and traffic jams, a net negative for every potential road user. There is no amount of roads you can build that prevents this tragedy of the commons. Every major city in the US has traffic jams. A city with "good" traffic is one where those only happen for an hour in the morning and an hour in the evening, and only at certain points.
The trouble with trying to build your way out of traffic jams is that housing and driving patterns always shift to consume everything to capacity and beyond. There is also the cost in terms of money, environmental impact, noise and space, if you care for such things.
What's the fix? The fix is to charge for the use of roadways. Only then will transportation and housing patterns emerge that leave roadways below their peak capacity during peak usage. People will still get places, and conduct active lives, but the patterns around accomplishing that will change. Housing patterns will change such that in general it's not so necessary to travel so far. Vehicles will achieve higher occupancy rates through carpooling and more usage of public transit.
Why haven't we adopted this yet, if it's so effective? Because it requires collective action that violates the highly individualistic US ethos. Admitting that you're a part of a bigger problem just isn't something that type of thinking does well. And so allowing yourself to be taxed to disincentive that behavior also isn't accommodated by that type of thinking. It's not the simplest jump in the first place (though well within human reasoning capacities), so a small mental block is all that's necessary.
But now there's a surprising new ally, Uber and Lyft. You'd think at first that Uber and Lyft would be against any policy that would add costs to taking an Uber or Lyft. But Uber and Lyft are driven by competition with taxis, personal vehicles, public transit and each other. Small individual transactions aren't the issue here. Prices can rise if they rise for all participants.
Taxis and personal vehicles get hit by a congestion charge just as much as Uber/Lyft. Public transit comes out the big winner, but while Uber and Lyft unintentionally compete with public transit, their stated goals are to compete with taxis and personal vehicles. Public transit is actually important to creating the environments in which Uber and Lyft can win out in their bigger battle with personal vehicles, so they don't have much incentive to intentionally target public transit in with the ruthless competition they unleash elsewhere.
As they become larger, those two entities have more incentive to ensure that road space is used effectively. The individualistic viewpoint is lost in the sea of Uber or Lyft's user base.
Another motivation is that political winds are not in Uber and Lyft's favor. Some kind of regulation is coming. They are far better off advocating for a change that's going to impact personal vehicles and taxis too than waiting for one directed solely at them.