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.