If I had to guess, this would have been either a request or something they just wanted to do for one of their "Developers Plus" developers:
Developers in this group have signed agreements with Hubitat and are allowed to charge for their apps and drivers.
I can think of one in particular but won't bother naming names. And it could still have just been something Hubitat wanted to do, perhaps to encourage more such developers who might prefer a closed-source integration for any reason, as @sburke781 hinted at above.
The idea doesn't seem totally odd to me--after all, most of the built-in drivers, plus the bulk of the platform itself--is closed-source. But the difference there is that I can count on support when I need it. I really don't see most community developers on here being likely to go this route. I could be wrong about that, but hope I'm not; again, my assumption is that this was done with the aforementioned group in mind, even if anyone can use it (though I think Hubitat has to put your URL in an allowlist first).
I don't plan on using any third-party apps or drivers that are closed source (and I don't plan on doing this with any of mine). I could see me making a rare exception for myself if they moved something like SharpTools or ActionTiles to be "community"-supplied instead of built-in (they're already closed, and the companies have enough of a reputation behind them for me to trust them). Otherwise, hard pass from me...but, again, I don't think (hope?) this will really end up being a big issue for most community code at all.