I expect someone was just trying to save money when the decision was made not to raise the manholes and storm sewer grids when resurfacing the city streets.
However, apart from an obstacle course while driving, trying to avoid expensive damage to one's car, there is hidden infrastructure under our streets. Water, sewer, storm drain, gas lines, and brick and mortar. The big rigs now moving through town can exceed 100,000 pounds.
My house, with a 2-foot-thick stone foundation, is 250 feet away from Fulton Street. The whole house vibrates when a heavy load hits those sunken manholes, enough to disturb a sound sleep. I can't help, but think after time the underground plumbing will succumb to the fatigue or stress.
Everything needs work sometime, but this will happen sooner for not making the manholes level with the street surface. It's not if, but when, and how much money.