In the late 80’s, both FHA and VA began requiring buyers to qualify to assume their mortgages. The main reason there haven’t been many assumptions in the past 25 years is that interest rates have been steadily going down and if a person has to qualify, they might as well do it on a new loan and get a lower interest rate.
Based on projections by Fannie Mae, Freddie Mac, the MBA and NAR, rates for the second half of 2017 and 2018 are expected to be higher. When interest rates on new mortgages are higher than the rates of assumable FHA and VA mortgages in the recent past, it becomes more advantageous to assume the existing mortgages.
FHA and VA loans originated with lower than current interest rates have great advantages for buyers and sellers.