I've seen several newbie accounts on Codeforces that have apparently over a thousand problems (some even over two thousand) yet don't seem to break the newbie barrier. I would expect such users to at least be very consistent at solving div. 2 A and B problems, but even that is not the case. So, my question is why do some people who solve very many problems not eventually improve? Is it a matter of talent? Not learning the right algorithms? A combination of multiple factors?

The intuitive answer to me is that they aren't challenging themselves with the problems they solve, but that doesn't explain why they don't become very good at solving easy problems. Indeed, some do become consistent at solving A problems, but I see many who don't often solve B problems, or at least not at the speed one would expect.