IDEs I think are a bit of a special case. Under the hood, it's constantly re-compiling and re-analyzing everything. That truly does take up a lot of memory and CPU. Probably not as much as if it were super aggressively optimized, sure, but still very heavy.

Full featured IDEs like this have always been heavy, as far as I know. It's only the pure-text editors without advanced full code analysis that can get away with low resources.