I've so often needed to understand what a library does when I call a function or use native or third-party class. In PyCharm or IntelliJ I can easily set a breakpoint at the call and dive into that third-party implementation. IntelliJ even will download and index the original Java source. No plain editor is going to give you that. The IDEs also allow code search in the vast sea of third party code, with approximate matching. If I only vaguely remember the function or class name I need, the JetBrains IDEs are going to find them for me.
Just two among many reasons to use IDEs.
I don't think the IDE should do "everything" for you, and you should understand how its building/compiling the software. But with statically typed languages and library definition hints. I think I would be wasting time searching docs if I didn't have the hints and type info. I can't remember everything I work with, it's impossible.