Microsoft isn't giving away it's exFAT patents. They are merely suggesting, that everyone licensed them at Microsoft's own terms. Those terms include becoming a member of Microsoft-sponsored patent ring and agreeing to it's terms and conditions: https://www.openinventionnetwork.com/joining-oin/oin-license.... The conditions can be changed anytime (!!) and the patent license terminates if you sue Microsoft or any other OIN member for any patent violations whatsoever.
Nikon, ZTE, Xiaomi, Samsung and thousands of others (basically all, who were or still are patent-trolled by Microsoft) haven't magically become members of OIN, and it's unclear if they ever will.
Google and Red Hat are members, but neither produces any devices with external SD-cards...
https://en.wikipedia.org/wiki/Sovereign_Internet_Law