You forgot to mention how much ADOM sucks, I`m disappointed.
The rest is (again) an example of trying to bend facts to your narrative and falling flat: if anything, it`s not being "close to roguelike" that hurt Starward`s Rogues sales - Arcen`s audience is mainly used to their slow, strategy, turn-based games and so didn`t really dig a twitch shooter (and said as much in the comments section).
As for "simple and easy to learn games": apparently Caves Of Qud sold as much as Sproggiwood when launched commercially despite the latter fitting into your description. But let`s not logic and facts get in the way of someone`s fixation, it`s too much fun as it is