Large majority who benefited from 2008 crash were not buying their primary residence. Whether they were real estate investors before 2008 or not many started getting into flipping homes or buying discounted properties and of course investors got many more opportunities to increase their real estate portfolios.
What stops one from getting into real estate purchase immediately after crash? It's the best time to flip houses. Once it starts going up, it keeps rising until the next crash. Here are some examples of people who didn't get burned by the 2008 crash, and who were doing 9-5 jobs (not millionaires/investors).:
1. Most their houses in late 90's or first couple of years of new millennium. Even after crash their property was worth twice or more of what they bought it for. And there were plenty of opportunities to buy second/third/fourth property before 2003-2004, when prices started to get ridiculous.
2. They were saving cash each month (whatever they could, $1000/mo or $2000/mo, for years while working their 9-5 jobs. It always comes handy to have $50K-$100K in your savings account which you could use as a down payment to buy a house.
3. They would never think of buying a house at high-interest rates, which people with bad credit or no proof of income were targeted for, and ended up as a main reason behind collapse. They would only buy at low interest rates, and would stay away from the market when it was red hot. They knew it would eventually crash.
To be sure, there were few people who did 1,2 and 3. Many did the opposite, bought when prices went sky high, never saved enough cash to buy second house and etc. But it was doable. It was a matter of doing the right thing and having a will to carry out with it.