This is a bit counter intuitive, but Euro style cabovers are much quieter inside than a 'conventional'. Plus cabovers can have air spring suspension, they're often more comfortable. The downside is much less space inside, which is a big deal for the long haul drivers in the states, whereas in europe, they rarely do more than a month at a time.
AFAIK nothing precludes having air bags on conventionals, it’s just optional / uncommon whereas it’s completely expected on euro trucks.
To clarify, the air bags isolate the cab from the chassis.
There is also suspension between the axles and the chassis which is 99% of the time air on the rear, leaf spring front.
I haven't come across a cab that is suspension isolated from the frame of a conventional, even though the axles are on air. Theoretically as the driver is in the sweet spot of a much longer wheelbase, rather than sitting directly over an axle.
> I haven't come across a cab that is suspension isolated from the frame of a conventional, even though the axles are on air.
They are very often on a simple suspension. The cab will have a pivoting mount at the front and sit on air springs in the back.