A copyright license is not a contract.
The OGL reads like a contract to me. It has provisions dealing with offer, acceptance and consideration, which are basic concepts in the common law of contract.
A licence to occupy premises is a species of contract. So is a licence to use someone else's copyrighted material.
Given that you apparently don't trust me, perhaps you'll trust
wikipedia:
A license is granted by a party (licensor) to another party (licensee) as an element of an agreement between those parties. In the case of a license issued by a government, the license is obtained by applying for it. In the case of a private party, it is by a specific agreement, usually in writing (such as a lease or other contract).
Of course gratuitous licences can be given - I can invite you into my home - but gratuitous licences can be withdrawn at will - I can ask you to leave my home at any time.
The OGL is not a gratuitous licence. It is a contract, as it makes clear on its face.
That they explicitly state that the license is perpetual.
Everyone knows this. But
making an offer to enter into a licence is not the same as
entering into a licence. I could, today, declare that I licence the Pemerton SRD under the OGL 1.0 to any and all takers. And then, tomorrow, I could withdraw that offer. Everyone who took up my offer in the intervening period would have rights under the licence. But once I withdrew the offer, no new licences could be created directly with me. Of course, under the terms of the OGL 1.0 sub-licences could be created with my licensors.
Not sure why you think Carlill is in point
Because it's still a leading case about offer and acceptance in the context of offers made to all the world. When
@Umbran and others say there is no contract with WotC because (eg) there is no exchange of documents between the parties, they demonstrate their lack of familiarity with
Carlill and similar cases.