That's essentially what all the fast transpilers do -- esbuild, babel etc. They don't typecheck the code at all, they just parse it and strip out the type annotations.
This means that you can run and test code that doesn't typecheck yet -- very useful during development. Also, production builds can run the typechecker in parallel with other build steps. That's how we optimized our build system at work.
But essentially, it's a design choice by the TypeScript team. They've decided that TypeScript shouldn't add runtime features on top of JavaScript, but instead should simply type JavaScript, and I think this has contributed to the success of TypeScript.
This means that you can run and test code that doesn't typecheck yet -- very useful during development. Also, production builds can run the typechecker in parallel with other build steps. That's how we optimized our build system at work.
But essentially, it's a design choice by the TypeScript team. They've decided that TypeScript shouldn't add runtime features on top of JavaScript, but instead should simply type JavaScript, and I think this has contributed to the success of TypeScript.