Despite their best efforts, the developers behind the game will not be able to maintain update parity between GOG and other platforms.
Sadly, this is the case for many games on GOG and not exclusive to Human Fall Flat. Why are those other games still being sold despite these known issues?
I get the strong impression that most of the games that have been pulled for from GOG for this reason were removed at the behest of the developers, not GOG. Which, IMO, actually reflects better on those devs than some think.
Obviously, it would be better for them to have been able to have kept up with updates on all platforms that they had initially committed to releasing on, but...shit happens. There are lots of inexperienced devs who didn't realize how much work was involved in keeping their builds updated in multiple places, and probably plenty of devs whose publisher pushed them into releasing in more places than they were necessarily comfortable with. Probably other non-asshole reasons for falling behind, too.
I'd much rather they admit that they overreached, and pull their game from a store or three, than just shrug and decide a site (where they already sell their game) isn't worth their time, but still keep accepting money from sales of a grossly out-of-date -- and possibly broken -- version on that site, without even so much as leaving a note that it would no longer be updated there.