IntelliSense is the best C++ code completion/"jump to definition"/"find all callers" feature available on any platform. The Visual Studio debugger is the best C++ debugger I've used. That's pretty much it, but it's enough.
Code completion and jump to definition isn't unique to VS. Pretty much any modern IDE offers it. GDB is an extremely powerful debugging tool that has a feature set that is really hard to match. It just has an extremely step learning curve. I can't really see much of an advantage of this besides getting to use tools you already know, which no doubt is a huge advantage.
No other code completion tool for C++ comes close to what VS offers, especially in speed. GDB is "powerful" but its UI is no comparison to VS, and when I say that I don't mean "GUI is better than CLI", I mean GDB's UI sucks. And UI does matter.
Code completion and jump to definition isn't unique to VS
of course not. But that is not the point, instead the point is those tools in VS are better than anything else out there. Having used a bunch of them I tend to agree. Definitely usability-wise the debugging experience just beats everything else.