With the CLA in place, it doesn't matter. All contributors already gave hashicorp a broad license for everything that they don't already own, so hashicorp has license to largely do whatever regardless of what license they use to offer it to others.
The CLA was put in place in December of 2018 [1]. Presumably contributions made before that were under inbound=outbound terms [2], meaning the contributing author licensed their exclusive rights under MPL 2.0, which is a file-based copyleft license. (see the chart at [3]).
Only the code in HashiCorp's own code is covered by the CLAs, not the code in the third-party dependencies it has. If said dependencies used copyleft licenses like (A)GPL instead of pushover licenses like MIT, that would have prevented what HashiCorp did.
