Fun point I read about this topic while back is that planes essentially cost the same amount of money per pound in the air, so building anything with two times the MTOW is an inherent disadvantage.
Apparently, a comment on the TSR-2 [1] was that it was too heavy. The problem was that the manufacturer misinterpreted this and instead of just going away and designing a smaller aircraft they spent a lot of money trying to make the existing one lighter.
It's not exactly practical to throw away a design and start on completely different aircraft! Also consider that the size was fixed by the fuel requirements and the wavelength of the sideways-looking radar. The second point was a dominant consideration in the earlier competition which led to the Avro 730 selection.
[1] https://en.wikipedia.org/wiki/BAC_TSR-2