Short answer: Republicans.
Yes, FDR establishing the FDIC (part of the New Deal) did make postal banks uneconomic, and LBJ phased them out, and they’re both Dems, but since Reagan, there’s been a push to privatize the postal service, driven by the R’s desire to see it either make a profit or fail — and if it does fail, to make a profit themselves on the corpse, leaving taxpayers to fund the utterly necessary but unprofitable parts.
Yet again,the Rs are trying to take away a public good that needs more financial support to break even in rural areas than in urban / suburban. And if you look at who votes Republican, it tends to be the rural area.
The same thing is going on with the Dept of Agriculture; they’re killing the rural development funding department. Looks like some corporate types want control of that ‘bank’, even though its funding is desperately important for people in rural areas.
Sorry ‘bout the tirade, but I’m full-on fed up and disgusted.