They are a test for people who are very strongly identified with being highly intelligent/skilled where their definition of "intelligence/skill" includes solvin

They are a test for people who are very strongly identified with being highly intelligent/skilled where their definition of "intelligence/skill" includes solving programming and computer science problems (and have the capability to achieve a good level). If that's your identity, then not being able to solve hard Leetcode problems (which, to my knowledge, are not even actually hard, since they seem to be easier than the problems in actual top competitions like the IOI, ICPC, etc.) is completely unacceptable and thus you will study and practice relentlessly until you manage (if you can); conversely, if that's not your identity, it's probably going to be hard to find the motivation to do so.