> You can literally just go download it off their website for free

That's cumbersome. The main benefit of platforms is comfort. Steam takes care of installation and updating, while often also offers some access with the community. Open internet has more choice and liberty, but for the price of more work and annoyance.

That the main reason why all big platforms succeed and the small platforms fail. Comfort is just too valuable.

OpenTTD has an automatic update mechanism already and its installation is as simple as could be.

Steam succeeded because of its store, which still has the best prices on the market. That’s their original moat. Their current moat is sunk costs. People have thousands of dollars in their Steam Library. At this point Steam’s advantages as software are negligible, especially considering its poor performance.

Easiest of all is `pacman -S openttd`.