Some commands don't use variables at all or use them in a way that doesn't
require them to all be fully valid and consistent. For those, we don't
want to fetch variable values from the remote system and try to validate
them because that's wasteful and likely to cause unnecessary error
messages.
Furthermore, the variables endpoint in Terraform Cloud and Enterprise only
works for personal access tokens, so it's important that we don't assume
we can _always_ use it. If we do, then we'll see problems when commands
are run inside Terraform Cloud and Enterprise remote execution contexts,
where the variables map always comes back as empty.
Martin Atkins