[emodendroket]

Because IntelliJ does a lot of work. Similarly, Visual Studio is not usually slow but sometimes it will mysteriously become so slow as to become unusable, or at least that was true a few years ago when I spent a lot of time in it.

[iLemming]

Visual Studio is a hosting environment for Resharper. And Resharper makes it awfully slow. IntelliJ compared to VS (even without Resharper) is like Emacs compared to IntelliJ.