Well bubble were caused by the huge whales who are buying a large amount of stocks or commodities.
Just look at the housing bubble. That was caused by millions of ordinary people buying houses that they ultimately could not afford
This is not even about that
If people only bought houses to live in them (i.e. as their homes), that might not have been such a big issue, after all (say, one house per family). But many people had been buying more than enough (so to speak) with borrowed money at that only to sell their property later when the price rose. Obviously, it couldn't but cause a real estate bubble to swell first and then burst it with people being unable to pay out their debts when the price of their "investments" plummeted like a stone