MTZehvor on 05 September 2016
I wouldn't call a series that's consistently sold over a million units "niche" (only one of its mainline titles failed to sell a million copies), but its appeal is unfortunately somewhat limited by the amount of thought and skill it demands from its players.
As for comparing it to things like Dark Souls and Bioshock, the fact that it's exclusive to Nintendo consoles seems to completely explain why it doesn't sell as much as those titles on multiple platforms. Bloodborne, which pretty much is a Dark Souls game that is exclusive to a single console, has sold 2.3 million units, and that's on a much more popular console than Metroid usually is.
