That's why C++ requires you to explicitly list the stuff you want to capture, and whether you want to capture it by value or by reference, and the least-keystrokes way to capture is to capture by value. Capturing a reference to something on the stack is an option which requires extra work.

C++ is predominantly a language that's oriented around value types instead of reference types. If you have a reference it's because you've taken extra steps to ensure the thing you have is a reference. As opposed to Java, Python, C#, Javascript, PHP etc where most everything is a pointer to somewhere.

Suggesting that C++ adopt GC to solve the problem of capturing references on the stack in lambdas is akin to suggesting that the Netherlands solve its biking/transportation problems by subsidizing cars and gasoline. It's not even wrong.