I think it is reasonable for a company to start OSS and then change its license. But it indeed feels like a rugpull for all the contributors.

That is why OpenTF is on its way to CNCF. To ensure it stays OSS forever.

There is a difference between "true OSS" like K8s, OPA, etc and "temporary OSS" (backed by a company) like what Terraform used to be, Pulumi, GitLab ,etc. Those can be changed in the future.

When developers chose OSS, they should consider if it is a CNCF OSS or a vendor backed OSS. What Hashi did is an important example.

(disclaimer - env0 founder here, co-lead the OpenTF initiative)