Why is the EVERSPACE 2 - Supporter Pack not available on GOG?

It will probably show up at some point. As i see it, Steam as the "biggest" platform usually comes first but GoG was usually supported very quick; they simply can not do so many stuff at once because not the biggest team.

In the support hierarchy i guess:
1. Steam
2. GoG
3. PS5
4. MS Store/ XBox SX

Just to remember, the "Supporter Pack" is just a collection of some cosmetical goodies and does not affect the game in any way. Still, i guess many of us are enjoying to support this team and may have fun using those goodies.

With the introduction of the new, to be released, "Titans update" and game version [1.2.42289], the supporter pack is available now on GoG and can be gotten here: https://www.gog.com/game/everspace_2_supporter_pack

Currently, everything is fully updated and "Titans" is coming soon: https://www.gog.com/en/game/everspace_2_titans