For sure it's different with trucks. Sometimes that works in your favour, like when it's bin day and you forgot to take the bins out last night.
In general though I don't really know enough to know why they can't make commercial vehicles quieter. In my experience at least city buses manage to be relatively quiet.
I'm impressed that your buses are quiet. In SF, the city buses rattle my entire house when they pass by a half-block away. It's more "vibration" than "noise", but the whole house shakes and I hear clattering of little unbalanced objects in the cabinets and so on. In the last 5 years I've never experienced an earthquake that shook my house any more than the buses that pass by every 10 minutes.
In general though I don't really know enough to know why they can't make commercial vehicles quieter. In my experience at least city buses manage to be relatively quiet.