There is this trend of coding questions getting harder. Around '12 2-sum was a question that is on-site worthy, now being the first of leetcode people expects dynamic-programming type problems in on-sites.

One theory is that the employers (especially big companies) just want the top X% of candidate by some arbitrary metric, and assume that top X% has to be capable enough to pick up new skills as needed. As people practice more, the questions get harder.

Then of course we'd mostly likely to never use the knowledge tested in interviews in real life. But hey, the goal is not to test knowledge, but to differentiate the top X from a pool of a thousand.