Your assumption (from your first comment) is that people only run bundling. That's not the case. People run bundling in parallel to type checking, rather than in series. You still get the type checking benefits without blocking your build on it and thus slowing down your dev process.

This is not a bigcorp thing. The Typescript compiler starts becoming annoyingly slow much earlier. I have a project that's one 2000-line TS file that already takes 1.5 seconds to compile. Not yet slow enough to be frustrating, but ridiculous for the amount of code.