I think it's because it disproportionately impacts the people who can least afford it. It allows the wealthy to continue to enjoy the convenience (relative to alternatives) of driving into the city while polluting and causing traffic at a price that has zero impact on their lives while it punishes those who already have much less and whose lives will be impacted by the fines and the often significant amounts of time they'll have to spend arranging and taking alternative modes of transportation.
That's a very hard sell when people all around the country are feeling continuous downward pressure on their lifestyle and financial security while billionaires are seen getting massive tax breaks and pillaging everything they want while escaping accountability for the harms they cause everyone else. Taking a basic task like driving into the city, something many people are forced to do for work, and punishing them for it while once again giving the wealthy a pass was certain to upset people. in fact, by forcing more of the peasant class off the roads it makes driving into the city much more pleasant for the people with enough money to not care about the extra expense. Taking from the poor to improve things for the wealthy resonates with a lot of people.
It also doesn't help that in other contexts, congestion pricing has already hit people's wallets and is seen as an exploitative business model designed to extract as much money from the public as possible. The last thing most people want is seeing congestion pricing and other price-fuckery infesting another aspect of their daily lives, which is why the pushback against wendy's implementing it was so swift and severe that the company had to backpedal even after spending a small fortune on the digital menu boards they needed to enable it.