Mortgage innovation was good for home ownership

In the United States, there have been two periods during which home ownership rates increased markedly: 1940's-1950's (47% to 65%) and since the mid 1990's (65% to now 70%). Why would there be so drastic increases interrupted by a long period of stable homeownership rates. Clearly this is difficult to justify with demographic changes, which are much more gradual than that. Another justification