Licenses != contracts, and well, the FSF's position has always been that the GPL isn't a contract, and contracts are what allow you to impose arbitrary limitations. Most EULAs are actually contracts.
Yes... a license can be granted via contract. I think the question here is whether posting a LICENSE.md file in a public github repo forms a contract (offer, acceptance, consideration) when a developer uses it. If so, I'm back to being unclear how "public domain" can really play a role. The developer is bound by the terms of that contract.
