Why was the map structure changed to linear in Barotrauma?

The initial version of the campaigns were very sandboxy, with no clear sense of progression, and no goals or objectives - you just wandered around the map doing whatever. For this type of campaign, the circular map where you could easily keep moving between biomes as you pleased worked well.

As the campaign started getting a more clearly defined structure and difficulty curve, the circular map no longer made as much sense, and we felt a more linear map fit the linearly increasing difficulty better.

I also have to point out that the old map wasn't intended to be a map of the whole moon: it wasn't a cross-section of Europa and you weren't travelling to the center of Europa. It was just a normal top-down map of a circular area on (and under) the surface, and you were travelling to the center of that area, which also happened to be deeper than the edges. The ocean on Europa is by most estimates at most 100 km deep - the center is much deeper, and you would need to push it through 1500 or so kilometers of solid rock and molten iron to get there. If Barotrauma was about that voyage, it for sure would not take place on a submarine. :)

The same goes for the current map too: it's intended to be top-down, and you're travelling east (or whichever cardinal direction "right" is in this case"). Here's a pic that might illustrate it better. It's a top-down map, and if you travel from the west to east, you're also going "deeper", down the mountain. The same thing with the game's map: you're travelling west to east, but the easternmost side of the map just happens to be at the center of a deep impact crater.

https://preview.redd.it/541f9a5rsfsc1.png?width=423&format=png&auto=webp&s=b70fbf3d4c09e1e66d10361f3812a2e55cf05ae8