I agree, it's always been unsettling to see any[] on hover, even though it gets typed in the end.

I think one reason might be to allow the type to be refined differently in different code paths. For example:

    function x () {
        let arr = []
        if (Math.random() < 0.5) {
            arr.push(0)
            return arr
        } else {
            arr.push('0')
            return arr
        }
    }

In each branch, arr is typed as number[] and string[], respectively, and x's return type is number[] | string[]. If it decided to retroactively infer the type of arr at declaration, then I'd imagine x's return type would be the less specific (number | string)[].

It depends on your tsconfig. An empty array could be typed as never[], forcing you to annotate it.