Why should colonization be about earning credits?
I hate hauling without danger, I hate repetitive actions, I am not into using my second monitor to watch shows while I fly my ship on the other one.
I am, therefore, not into colonization.
However, based on what I read here and there, some people are. They like to haul 22k tons of Titanium on their carrier, then unload, rinse & repeat, until they have completed their constructions within days.
Good, I LOVE the idea of the inhabited space growing, spreading, and hopefully leading to player-driven content, or FDev shaking up things in the future (maybe adding interesting features to a newly developed area of the galaxy, like new engineers, Thargoids showing up, etc...).
If all you care is credits, give a try to Exobiology, learn the ropes, get to understand the methodology to find the high paying bio-signatures, and by the time you have mastered it (in my case, 3 trips of 3-4 days each were enough) you will get so much money that carrier upkeeps or rebuy screen will mean nothing anymore (I found a system worth 350 millions of bios, which would have been 1,750,000,000 credits with first foothold...later found another where I was the first foothold and got 500,000,000 after a couple of quick scans. You will earn in average a billion credits every few hours if you do it right).
ROI is not the point of colonization. It's about building something, leaving your mark, if you like it.
If you do not like it, let the other players do it, and see what comes next.