Tolls are there to pay for the new roadwork(s) (and in some cases, line private company profits). Nothing more. Anything else is not effective, it's just prohibitive.
It's good to have any scarce common resource be bid for, rather than giving it to whomever shows up first, is willing to wait longest, etc.
If 150k people want to go, it's usually better that the 100k people who value the road the most get through quickly, instead of having a random 110k get through after a large traffic jam.
150k people wanting to go and being able to go is better than a quarter being forced to stay home, a quarter being forced to not go and another half being allowed to go.
In many places, congestion pricing is dynamic and tries to keep roads at the highest throughput capacity.
Here, it's a pseudo-static value chosen to try and push the roads to the highest throughput capacity. (There is some variation by time of day, but not by actual demand).
It has a lot to do with market mechanisms. This is stuff that's within the capability of a high school student to perform a reasonable analysis about after a semester-long class.
I've never seen a toll road decrease in price because no one was using it. Wouldn't that be the easiest place to test congestion if "market played a role"? Car number go up, price go up. Bing bong.
No, it might take a high schooler to read too much into it and pluck things out of thin air though.
It's okay if you genuinely think prohibiting something is effective at providing people with more effective usage of that thing. You'll be wrong though.
If 150k people want to go, it's usually better that the 100k people who value the road the most get through quickly, instead of having a random 110k get through after a large traffic jam.