In enterprise, you generally do.
You don't have to throw it away, just sell it, donate it or use it privately.

“Don’t have to” and “don’t” are different things. I’ve never been in an enterprise environment that kept PCs much beyond their 2/3 year service window.

In fact, they messed up and got consumer hardware once. They EOLd the devices at 6 months when they realized they only got a month of support.