I've been updating the game for over ten years at this point, adding new content, features, etc. It just isn't viable to release it as one time purchase if I want to keep working on it over very long time periods.
Steam is a cool platform, and I could even release it as subscription on Steam -- but it'd have to cost more there due to the heavy 30% fee valve charges. I don't think people would realize it was cheaper direct from dev than via steam. Also, I'd have to put up with constant review bombing of people having unrealistic expectations -- for steam gamers value is very important, and so most people there have a conception that indie games should cost basically nothing / wait for massive sales. But that's not sustainable which is why you see so many abandoned early access projects on Steam. The majority of steam devs make extremely little, nowhere near enough to live off for what they sell their games for. Mass market games can do very well, but super niche stuff like this isn't going to perform well there. My options for Steam is that I could price the game unsustainably cheap and be out of business in six months, or price it at sustainable prices and not sell anything there and it be a waste of time with a 0% review score. So I like steam, but I view it as no way to succeed there.
I am certainly willing to add steam-inspired features such as achievements, etc though!