airac,
Unless you're at an extremely quiet airport, could you really stop any other movements (including aircraft taxying, operations vehicles carrying out runway / taxiway checks, any other service vehicles free-ranging on taxiways where they might possibly infringe the runway)? It's fine expediting the inbound's approach, but you'd then be possibly delaying a departure by several minutes beyond the point at which you could have released it anyway procedurally!
Terrain separation is theoretically taken care of when an aircraft flies the centrefix approach, as the crew and the FMC should be aware of the MDAs throughout. But they should also be aware of MDA or approach descent fixes on, say, a VOR approach. Two recent(ish) and publicly reported descents below minimum altitude on final approach were resolved; one by ATC monitoring and go-around instructions, the other by GPWS. That's surely enough for the regulator to avoid changing the status quo for the moment, in my opinion anyway...