I've always accused those games of being "NES hard". Where it's about the fact that you're supposed to die, retry, memorize, repeat. They definitely have a lot in common with the original Ninja Gaiden and Castelvania games

In fact there's been a few arguments on the internet (and even here, I believe) that Souls and Bloodborne fill a gap left by the lack of any decent Castlevania games recently. Where you might say Bloodborne is a 3D less forgiving Symphony of the Night or something

I guess they fill a lot of niches for people. WRPG, JRPG, Metroidvania, NES difficulty factor, beautiful and depressing