Edit: found something: https://www.hashicorp.com/blog/hashicorp-adopts-business-sou...
This was a major blow to the participating open source community. The license bow used is also vague and untested.
This encouraged at least 4 companies to launch terraform-cloud-like products, and rather than compete and provide better service, Hashicorp responded by saying "take it or leave it, internet!" and they closed the open-source license on the interpreter (BUSL)... At my previous company we were driven away from terraform cloud and into the arms of env0 ... when it often takes 10 minutes for an execution to begin and you have no other executions in progress you realize that the terraform cloud SAAS product is just a total joke...
Those who take this to the next level by offering Enterprise like features such as change window and approval gates from Jira/ServiceNow will land whales.
Before the license change, another project (Pulumi) built something that was basically a thin wrapper on Terraform and some convenient functionality. They claim they tried to submit PRs upstream. Hashicorp loudly complained about organizations that were using their source without making contributions back when they changed to BUSL. I wasn't close enough to be aware of details there, but maybe there were other groups (I can think of Terragrunt, too, but I'm not sure they're included in the parties Hashicorp was complaining about. Terragrunt did side with OpenTOFU after the license change, though). This also means cloud providers can't stand up their own Terraform cloud service product as it could interfere with the BUSL license.
When the license was updated to BUSL, several contributors forked the last MPL-licensed version into OpenTF, then renamed to OpenTOFU. Some say that Hashicorp should have gone full closed-source to own their decision. I think they knew they were benefitting greatly from several large corporations' contributions for provider-specific configuration templates and types.
Then, earlier this month (two weeks ago?) Hashicorp brought a case against OpenTOFU claiming they have stolen code from the BUSL-licensed version, with OpenTOFU outright denying the claim. We'll see how that shakes out, but it shows that Hashicorp wasn't merely concerned about copyright & business/naming concerns (a big part of why other BUSL-licensed projects chose the license). I don't know if the upcoming M&A had anything to do with their license decision but I kind of doubt it? Maybe others here have more context or are more familiar with matters than I am.
I'm sure IBM Cloud's Vault offering was part of the decision, but from where I was sitting, it didn't look like the reason or even the primary reason.