Wasn't it also the case that the so called Military Industrial Complex, which then as now wielded immense influence , gave the nod to the politicians to 'lose' all the equipment so that new (and profitable) equipment would need to be ordered from the tax dollar to replenish the forces and to be ready for the next devil at the time, namely Ivan and his communist hoards ?
As to preservation, the mud/silt encasement does have wonderful effects on certain materials, but I'm of the understanding that at deeper levels, the salinity of the water reduces and that combined with the very cold temperature and no UV leaves certain items minimally untouched by time. As long as the metal frame of the aircraft was intact and the ID plate intact it seems like they're good to go in terms of restoration projects. Those buried Spitfires in Burma that were never found, were apparently likely going to be in a right old state, yet had they been found were to be deemed authentic despite the majority of new components used in the rebuild.
SHJ