There are myriad circumstances in which there are no viable forced landing options after an engine failure in a single-engined aircraft. Just one recent example out of many I've observed, first-hand:
Not that long ago a VFR route was added to the Canberra VTC. The route goes from Cotter to Tharwa, not above 3,500' AMSL. Have a look at the VTC and note the spot heights of the granite adjacent to that route, which roughly follows the Murrumbidgee River.
I flew it. Once. I was jiggered if I could spot any viable forced landing area anywhere along that route. And at the height AGL, there wouldn't be much time to do a leisurely couple of orbits to look for one anyway.
By putting it on chart, 'the powers that be' could reasonably be assumed as having endorsed it as a safe option. For my part, I don't think it is, at least not for single-engined aircraft.
The terrain under the routes in and out of YSBK is now 8/8ths of McMansions and Motorways. Good luck in finding a viable forced landing area within the 60 seconds or so you'd have after an engine failure along those routes.
If the cause of the engine failure is attributable to the pilot - e.g. fuel mismanagement - that's a whole different 'ballgame'.