Because doing shit like this and still losing is annoying as hell.
I mean sure?
But I’m not exactly sure if there would have to be any mid-rank III-IV bomber aircraft currently below BR 6.7 that is nuke carrier capable except for the B-29 itself at 6.7 currently (which was also literally the only WW2 plane that could even carry nukes at the time).
For low tier, it might also be extremely unbalanced as the B-29 Superfortress is still more advanced than other WW2 bomber aircraft at the time and can also deal with slower monoplanes or bi-plane fighters with computed controlled remote .50 cal gun turrets with 4 x powerful 2000HP+ Wright cyclone engines that might even allow it to outrun certain planes trying to intercept you in some instance despite being a massive bomber.
Lancaster was tested and it was nuclear Capable with small warheads.
There fine where they are, and even “if” you had a nuke option there is no guarantee you would of made it to the drop.