We just call them conventionals as everyone builds them (even Volvo here in the US).

Bit of history, until 1976 the US had a maximum combination length restriction of 65 feet. For a standard 53 foot long van, that only gives you 12 feet of tractor. While you may be able to pull that off with SWB day cab in a conventional config...long haul drivers want sleepers and as long of a wheel base as they can get. 1976, fuel crisis and just about anything that could be done to lessen fuel consumption was done (national speed limit of 55 mph instituted, calls for manufacturers to build more fuel efficient vehicles, etc) and conventional trucks are typically more aerodynamic thus slightly more fuel efficient so the easy solution...extend the combo length limit to 75 feet. When you can haul a standard 53' van...have a long wheel base and a decent sleeper with a conventional tractor...why dick with cabovers?

It's truly a case of they've become rare because Mack, Peterbilt, Kenworth, Freightliner, International, GM, Ford, etc stopped making them simply because due to the lift of length restrictions, they simply weren't selling. Granted, you can still by a cab over Mack and Freightliner today...just not for tractor use (Class B application) though you could probably take an Autocar ACX as a 6x4 tandem drive chassis and add a 5th wheel to it. The cab profile would be lower to the ground compared to a traditional White-Freightliner cabover but the cab is relatively unchanged (in fact, the severe duty Autocar trucks have only updated the cab from the 1960's White-Freight cab in the last 10 years or so).