I've wondered about that. My parents bought their house on an assumed loan way back in 1968. I'm under the impression that you would have to come up with enough equity to cover what was already paid on the home. I think that would be much harder to do than the basic 20% or whatever down for a standard home.
I am happy to see where they are starting to crack down on large investors gobbling up numerous homes for resale or rental purposes. That to me at least is what is holding back first time buyers or even those of us seniors who may have sold a home to downsize, then try to get back into the market after renting for a few years.