The housing bubble didn't destroy the economy. Shutting down old factories and laying off those workers destroyed the economy. The housing bubble sent all those laid off workers into bankruptcy and foreclosure. But they were already in trouble.
The collapse of the financial sector was due to massive fraud executed through exploiting flaws in the new MERS method of mortgage processing (security sucked when they first went to online processing in 2003). Like you say, a real mortgage is backed by a house, even if the bank loses money they don't lose much, as long as they end up with the property. But when fraud was executed, fake mortgages, identity theft or fake borrowers, and self-insured Title that... closed a quarter billion in a couple of months, then vanished... that's what was stinging the big banks for tens of billions in write-offs per quarter in 2005-2007. The big banks stopped the bleeding by shutting the entire industry down, which resulted in property values going under water nationwide. It also tanked the stock market.
Obama's recovery was fueled by all that capital the mafia stole from the banks, they turned around and invested it into new factories with automation... hence, the jobless recovery. Trump says he's going to bring back jobs to our fallen middle class... believe that when I see it.