There's way too much money in the hands of the wealthy. What are they going to do with it all? Invest in the stock market. All the good investments are overvalued. All the bad investments are have been saturated too. What else can they do with all of that money. They gotta put it somewhere.

So they put excess money into real estate. So the price of real estate has been driven up so much that it's over valued like any other avenue of investment.

The stock prices being overvalued isn't good but isn't something that'll affect regular people. But their real estate investments being over valued? Well that real estate isn't an investment to someone that simply needs a place to live.

And that's the problem, the price of housing is priced above what the people what people outside of the investor class can afford. And the investor class wants a return on their investment in the overprices real estate (that they collectively drove the price up on) so charge a lot for rent. Of course maybe if people moved to another area that would put downward pressure on the rent prices. But AirBnB is there so if this happens they can still get income from that when no one can afford the insanely high rent.

So the overarching problem is the wealthy have wayyy too much money and are dumping their excess wealth into real estate and pricing people that just need a place to live out of the market. AirBnB isn't the cause of the problem but it makes the problem worse.

One of many problems caused by the unwillingness to simply tax the wealthy.