Game devs want fast iterations above everything else, with performance being a close second. c++'s "toolchain" makes those iterations prohibitively impossible, even with decades of workarounds with hot reloading and extravagant methods to keep compilation times down.

If you're a AAA dev you give up a lot of that iteration because performance overtakes you, but there's little reason some indie 2d platformer will want to deal with even 30 second iteration times (which would be blazing quick for a AAA setup). C# is a mature, familiar environment for devs with similar syntax to C++ that can get decent performance as long as you maintain some discipline (for starters, no LINQ)