Would this not be pretty much the same thing? Releasing a patch is maintaing the game and also supporting the game? Basically your just paying for dev time... as far as I know GOG doesn't charge anything to release a patch.

What do you mean by this exaclty? As far as I know GOG doesn't charge anythng to host a game here... other than there 30% cut in each sale.

No doubt, but I would still think unless your game is really niche... that it would still be profitable. Less popular games that Subnautica seems to be able to make it worth there time to release and support their game on GOG.
interesting... I don't put as much stock in SteamSpy as some do but none the less it's all we got. I would probably put it a little higher as it's just a rough estimate. Developer Lars Doucet stated back in 2013 that Defenders Quest generated 14.5 percent in sales on GOG when compared to Steam (8.5% when compared to total sales from all stores). So I would put GOG on average around 10 - 15% of Steam sales all things being equal. Which is actually not bad.

I think that will continue to increase with more high profile releases here (expecially if CDPR does something crazy like make Cyberpunk 2077 GOG exclusive or decides not to release Gwent on Steam).

Something else I didn't think of before is this. Maybe a developer does not release on other platforms because he wants to concentrate all the sales on steam in order to make the game a steam best seller. I don't know what would be the advantages to this.

It doesn't. No Workshop for Subnautica on Steam.

Outcast sadly did not sell very well on Steam, according to steamspy about 5 thousand copies - while the numbers are not exact, they are good indicators of the real sales volumes.
Hopefully Outcast will be able to make at least the same numbers here on GOG though - I am doing my part in that regard soon ;)
So sales on GOG, even a few thousand units would be very worthwhile for the Outcast developers right now; they'd effectively at least double all their PC sales by releasing on GOG.

Now, if you take a look at Subnautica, it has already sold 2M units, which gives us a whole different perspective.
Selling a few thousand units compared to 2M is indeed not worth the effort, when they already have a VERY demanding steam community to support and probably tons of patches to make to keep up with demands.
Right now, they are probably hiring like crazy to deal with the unexpected success/support flow; selling 5 thousand units in addition to the existing 2M makes no business sense, considering the resources needed - when they realistically can't spare anyone for a task only affecting a very small number of their current userbase.

Numbers floating around say GOG sales are 10-15% of steam sales on average, but I am pretty sure it depends on the game, e.g. RPG, RTS, adventures could actually do way better here on GOG, than on steam, while something like Subnautica may do worse as it's not necessarily for the core GOG audience.

I think we'll have a chance to see the game here though eventually, once they have enough resources and the patches settle down a bit.

maintenance = bugfixing, patching, possibly additional content. technical thingies in the background
Support = answering questions, forum participation, answering emails. outward facing to customers

sorry, sprelling mistake. it is supposed ot be liaising, not leasing.... it is all the B2B communications between partners. someone need to do those also.... ideally

aye, and when you have an publisher they do most of this stuff for you so you do not need to bother (but then you do get a smaller cut yourself). However, Subnautica is self-published so all is done in house.

So the question is at what point is is worth the effort? you may make a few pounds more, but is it really worth the hassle when you instead could be planning your next game?
indeed. Being on the bestseller in trending list on Steam is becoming THE best advertisement today. So in the first weeks of sale, it makes little sense splitting up your users-base, and therefore risk not getting into either.

Subnautica has a story and the option to switch off the survival elements.
I have the game on Steam but I was very much hoping that it would come to GOG as I was planning on gifting it to some friends (I generally don't gift Steam games to friends).

Hmm.... sad. The game looks very interesting. But Steam-only = no buy for me...

When I saw the trailer for the game, I was like: Meh, another one with such a stupid haircut.

I would be never ever be caught alive with such a hairstyle, even if I still had the hair for it...
So they can keep the game.

have you told the dev this?

You can't even see your character model in the full game. The best you can hope for is a glimpse of your diving fins as you backpedal or your shadow(which looks freakishly anorexic) on the sea floor.

Not yet... was at work and didn't have time to search for a way to contact them.

there are very few FPP games where you can see your character.... they kind of stop being first person at that point...

You could see yourself in Duke3D. They used mirrors.

there may be mirrors in Subnautica as well?