Microsoft did the digging with their C++ standard library, which is derived from Dinkum's STL.
I observed that a bit with Sun and Solaris/OpenSolaris where in the final release was one component missing.
So even with will this won't come for free.
(Which even them, they offer free as in beer).
To make the brand attractive, free/open source is best.
The "good" reason: Because relicensing of old software is hard and while they want to make it available (to strengthen their position in the developer community) See also my comment in https://news.ycombinator.com/item?id=24048633
You make a brand attractive by offering a good product, good support/service, and then marketing those points.
I try to use as much OSS as I can. But free/opensource isn't the most attractive feature to everyone. And I'd say the success of so many proprietary companies is proof of that.
After all, if the remote development feature is based on a centralized server (owned by MS), the license check will be performed on that server. And if no centralized server is in play, suffice it to say, anybody sufficiently motivated could reverse-engineer the plugin, remove the license check, and go on using the feature for free.
So they control the value from those closed features to only be used to enhance the VSCode and VS brand.