Its still open source. You can still view the source code. That's what open source is. The change here is the restriction on providing Terraform as a service in the form of a Terraform Cloud competitor. This seems to be a very direct response to Amazon introducing a service for hosting terraform modules, storing terraform state, and applying changes.

I don't love this, but they're also not restricting anyone's comercial ability to develop products using terraform like a banking app, a link aggregator, or a e-commerce platform. All you're restricted on is providing an IaC service where you directly profit from running someone else's terraform for them. This is the same license the MariaDB creators came up with when they felt burned by Oracle but did want people to be able to build closed source products using their database without profiting from providing their db as a service (this is why many self hosted projects use Maria instead of MySQL) which is why AWS can't offer maria RDS instances.

AGPL wouldn't help them keep developing terraform the way BSL would because their business problem isn't that no one is contributing back to the code, their problem is a $1T market disruptor just turned their Sauron eye towards Hashicorp's $5B shire and offered their own shire for less money behind the black gates. All after for many years directly benefitting from Hashicorp's existence and giving them white glove treatment as a result. And yes I'm aware that in this analogy Hashicorp is probably one of the Nazghul being corrupted.

Like I said. I don't love this license change. But like I said. Hashicorp doesn't have a code contributions to Terraform problem. They have a funding their business and development problem