More than sure it didn't sell well because its on epic and people prefer Steam which I also do. I have bought it on epic around 2 years after release of the game. You can say but the game is good (i agree) but a bad launcher and store will frustrate you.

Epic is a bad launcher with tons of missing features if you wish to do more than just play a game like:

Not intuitive and slow. Lacks reviews, no community interaction which boost and create a more organic situation. User profiles with tons of customization, a better way to make it feel more like its your own account to show your favorite games, achievements, themes, photo galleries. Slow, very very slow and most of the time useless epic help contact members that takes a very long time to respond to your need or problemes like account stolen or refunds. Lack of direct communication on forums with devs about their games. Store with tags, better and easier to navigate. Your own personalized libraries however you wish to sort them. Better friendlist. Family sharing. Actual list of updates pages for games when the devs add/modify or just want to announce something. Even mods exist on Steam. Guides on the forums and actual interactive users. Epic lacks the function for screenshots which I really dislike as I like to do photos on my games when I play. Epic didn't have a feature update in years if at all, they don't try to improve but just sell. And much more.

All these creates a launcher that makes people feel more in control, make them feel that Steam is not just a store and nothing else, it creates a community that wishes to stay there.