I that you're right that it's just IntelliJ doing too much. Similar to how the Slack app's formerly astonishing memory consumption was because it was trying to retain all of Giphy in memory for all time.

Somewhat related, back when I was a C# developer, I spent a long time being confused over the community's somewhat polar opinions on whether Visual Studio is slow and bloated, or lean and snappy. Eventually I realized that the difference of opinions was because some people's employers buy them copies of ReSharper, and others don't.