A combination of fiscal policy (money is literally expensive at the moment, as central banks raise interest rates to combat inflation) and fear (a lot of people have been expecting a recession any day now for the last year, though it keeps getting postponed, and may yet be the recession that never was; while a good few countries dipped briefly into technical recession this year, fear of another proper global recession does seem to be abating a bit).

The over-simplified answer is "The fed started upping interest rates, after having held them ridiculously low for about a decade."

There's arguably more to it than that, but when people talk about "cheap money" they mostly mean "low interest rates". If you just Google terms like "end of cheap money" you'll find lots of discussion on all of this.

Some examples:

https://www.ft.com/content/6d312b6c-9f74-4816-ad7e-7e797c5e0...

https://www.bloomberg.com/news/newsletters/2022-11-30/what-s...

https://fortune.com/2022/12/28/investing-outlook-2023-fed-in...

https://www.reuters.com/breakingviews/end-cheap-money-reveal...

and so on.

basically the mechanism that the Fed uses to keep interest rates low involves creating a lot of new money and using that to buy bonds from other people, manipulating the market for bonds (high priced bonds = low interest rates).

Most of those bonds were government treasuries, but other bonds were corporate bonds - sheets of paper that say I'll pay you back in 10 years - and sold directly to the fed for newly created money. so the corporation printed money and got newly created money in exchange. they just have to pay it back in 10 years at like 2% interest a year. Many of those corporate issuers parked that money in private equity firms, or were private equity firms themselves, if they weren't directly hiring employees for pet projects - the private equity firm would be investing in newly formed pet projects.

All of that has stopped now, as the fed stopped buying bonds and doing the most to get interest rates high. Doing everything except selling the bonds they bought.