There's a variety of reasons, not just one specific overarching issue that other studios fail to understand. It's often that they take the wrong lessons from FromSoftware's design, whether that's just making the game hard and thinking that's what makes soulsborne games work, or relying too much on one specific gameplay element that was only one aspect in a FromSoftware game. A lot of soulslikes just give the enemies tons of HP and call it a day, like you mentioned, and that rarely works in their favour as the challenge ends up turning into tedium.
One example that I can think of is Nioh's world design being quite dull and fragmented, where each location felt completely separate from each other rather than part of the same world. Sometimes, however, the problem can simply be a limited budget, like with Asterigos: Curse of the Stars. It has some nice ideas and does pretty well within its limitations, but you can definitely see that they were working with a lot of constraints.








