Apparently it's happening in Sheffield too. Old trees do sometimes have to be removed, especially near roads. Here they just fall over and cause traffic problems.
Sheffield Council, as I understand it (my understanding is limited!), is planting young trees to compensate for the ones being removed. It is being said that the new ones are being planted in the wrong places, i.e. (again, as I understand it) not on the streets where the old ones were.
I think part of the reason for tree removal in cities is that councils can't afford, or claim they can't afford, to deal with all the problems old street trees are causing: blocked drains, broken kerbs and dangerously root-lifted pavements, etc.