Ever see those mulch volcanoes piled high around trunks? Read an article that called it "slow death by suffocation." It's the same bad idea as planting deep, just above ground. The bark stays wet, rot sets in, and roots start girdling because they can't get air. I've seen maples with their own roots strangling them a few years later. People just don't get how much damage that little mound does.
Actually the city crews often know better but they're rushed. The real problem is the landscape company that installed it. They get paid by the job, not the hour, so they bury trees fast to move on. Seen it a hundred times. The city just accepts the work without a proper check. It's a system failure, not always the workers.