This isn't the Chrome browser itself; it's just an installer for Chrome that opens to Google's Chrome download page.
The description in the Store says:
"This installer helps you get the official Google Chrome: A fast and safe browser from Google.
"[Note to Windows 10 S users] Windows 10 S is incompatible with apps like Google Chrome. To use Google Chrome, upgrade for free (for a limited time) to Windows 10 Pro."
I'd guess this move is aimed at non-technical users who somehow may not know they can just get Chrome directly from Google, and instead look at the Microsoft Store as a place to find their apps. (Shrug?) Or maybe the mass of bad Chrome clones in the Microsoft Store led Google to take drastic (and/or dastardly) measures?
Update No. 3: One Google engineer seems to imply this all happened because of the large number of clone/rogue versions of Chrome in the Microsoft Store.