The purpose of any software license is to permit you to do things that, in the absence of a license, would otherwise violate the authors' copyright. This is unrelated to whether or not the author chooses to accept contributions. No FOSS license requires the copyright holder to accept third-party contributions upstream, nor do they directly discuss this topic at all.

Licenses are not invitations to collaborate. That simply isn't their purpose. This is why CONTRIBUTING.md is a completely separate document.

Most of the popular "OSI-approved" licenses predate the OSI's existence, so there's no plausible argument that adopters of these licenses are opting-in to a collaborative social movement with an "unwritten social contract" en masse.

For example, the original motivation for the MIT license was simply avoiding legal overhead for software that wasn't expected to have much financial value: https://en.wikipedia.org/wiki/MIT_License#History