In Real Life Nothing is Really "Free."
You may not have to pay a fee for it up front, but you have support expenses, training expenses (even if its just "buy a book,") ramp-up time (your salary isn't free,) power to run the hardware, hardware to run it on (or cloud cycles to pay for,) a place to work out of to manage it all (or pay somebody to manage it for you.)
Even "totally free" software--as in "free price" and "freedom to change it to meet your needs" isn't actually totally-free-of-costs.
Likewise, you might not have to "pay" for a license to get Hyper-V Server, but is most assuredly not free.
This doesn't even begin to get into the discussion of "free" to acquire vs. "free" as in "Freedom," either: I'm only talking about a rational business discussion of cost. In business, nothing is ever free.
The main reason "free" is on the table is to get IT admins to try the product on older systems to learn the power of it and advocate for it in production. That was VMware's strategy, Citrix's, and its now Microsoft's. It is a wise-strategy: I've got it downloading right now and will try it (albeit as a guest under my vSphere environment) precisely because there is no big PITA to get my hands on a legitimate copy.
