The boomers heading into retirement situation is a reflection of 40-50 years of economic policy and has no connection with recent "cheap money".
Actual investment in single family and apartment housing is almost entirely tied to its low risk/return ratio compared with (the perception of a lack of) other options for investment at this time. The money sloshing around for investment is as much as function of the effective privatization of retirement funding as anything else.
The short term rental market is in part the perfect expression of how a relativel small number of wealthy individuals can totally distort a market to follow their own preferences, and reflects income/wealth inequality and lack of regulatory enforcement (they're freakin' B&B's people!) as much as anything else.
Cheap money has almost nothing to do with any of them.
Mostly to keep juicing the economy, which has steadily been needing it more and more to grow/less responsive to stimulus.
Folks I know who have done the AirBnB route were often getting mortgages and buying properties to let out, using the short term cash flows to pay the (low interest rate) mortgage.
Which makes sense as an investment, because the mortgage was cheap (cheap money) compared to current cash flows.
It has become more and more pervasive, until it stopped being able to make money due to saturation. Younger folks traveling around during Covid using AirBNBs helped (they were trying to avoid lockdowns and ‘dirtier’ hotels), but not sure how it is going to play out now.
Anyone who had a 30 year mortgage they got then is going to do pretty fine though as long as they have cash flow.