I'm not sure why that would be the case.
In the case of stretches, you have to insert segments before and after the wings in either case.
In the case of engines, increasing diameter size is a significant problem with underwing engines. Even before the 737 max kludge that killed hundreds, you had cases where ground debris was a problem with the bigger fans. Which is why 737-200s with their tiny low bypass engines are still used in the Canadian North on gravel runways.
In many ways it ought to be EASIER to stick bigger diameter engines on a tail engine jet than an underwing one.
I agree, you can successfully stretch tail-mounted engine designs as was successfully done by on the 727, the DC-9 (5 times!), and by Vickers themselves on the VC-10. The issue is that the added fuselage structure needed to support larger engines in a tail-mounted arrangement usually require more engineering costs and typically weighs more than the same modifications to a wing-mounted design, thus reducing efficiency.
The design also ends up being physically longer as you can’t place a full passenger cabin between the engines on a tail-mounted design due the space constraints for fuel lines and electrical runs. A 727-200 is 7 feet longer than an A321, but carries fewer people as the cabin isn’t as long. This isn’t necessarily a problem for smaller narrowbodies given their smaller dimensions, but would be an issue at some airports with constrained ramp space for a hypothetical stretched widebody design with tail-mounted engines.
Another consideration is that the engines are more accessible for maintenance on a conventional wing-mounted design. Generally you can access the engine from the ground or with a standard 8ft step ladder on a wing-mounted design. With a tail mounted engine, you’d need a manlift, boom lift, or special scaffolding. I recently watched a TV show where Alaska Airlines maintenance personnel had to change out an 737’s engine outdoors in Anchorage in winter. Alaska has a portable inflatable structure with which they surround the engine to allow the maintenance crew to perform the engine change out of the elements. Try that on an MD-80.
Finally, the global commercial infrastructure has been built up to the point where the benefits of a conventional design in terms of a lighter frame and maintenance access outweigh the relative benefits of a tail-mounted engine arrangement. The 727, DC-9, and the original 737-200 all had short, squatty landing gear (and optional integrated air stairs) because they were expected to fly to smaller airports which at the time didn’t have the infrastructure (such as airstairs or bag loaders) for larger aircraft like the 707. That’s changed. With the much more robust airport infrastructure around the world, it’s easier to take advantage of the conventional design for its inherent lighter weight and simply design taller landing gear to accommodate higher bypass turbofans. You are indeed correct that 737-200s with gravel kits soldier on in the Arctic because the larger high bypass engines suck up too much debris, but that’s a tiny proportion of the market.
From a purely aesthetic standpoint, I prefer the T-tailed, rear-fuselage mounted-engine designs. And it’s hard to beat the quiet cabin in front of the wing on a T-tail bird like the 717 from a passenger point of view. Unfortunately the wing-mounted design has proven itself to be more efficient than the tail-mounted design given modern technology and today’s marketplace.
