It would never be on steam, Unixmad is making enough cash as it already is.
It being on steam doesn't necessarily mean it will have an increase in players, there are certain games that do poorly even with it being on steam.
Graal isn't one of those games people would want to play when there are far better games with proper customer service.
He doesn't have to risk it, it's a gamble that is honestly not worth the time.
I also believe he doesn't like the idea of Steam taking a minimum of 30% profit.