> I think the problem is that people aren't cloud capacity you spin up / down
Visa issuance the world over are designed to work exactly this way: to scale (foreign) labor up and down as needed. You may scale just the intake (if it is for permanent residency, like the much praised point-system used by Canada), you can also spin up or spin down the entire temporary visa labor force by changing the renewal and first issuance numbers.
[Citation needed]
I don't think any country invites and then carries out a massive purge of existing labor as it sees fit.
If it does, then it won't be appealing to the class of person you're seeking to attract.
> [Citation needed]
Perhaps you could attempt to steel-man why point-based immigration allocate and de-allocate points for certain professions over time? Or why temporary visas exist in the first place.
> If it does, then it won't be appealing to the class of person you're seeking to attract.
Such is the nature, complexity and self-contradicting character of any large-scale public policy; and it's "classes" (plural) because immigration cuts across social strata, not just your software and service industry "rockstar" geeks.