Unable to pass SIGTERM to a process in a bash script

Question

I'm running Terraform from a script in a pipeline. I would like to ensure that if the pipeline job is aborted, Terraform receives SIGTERM.

_term() {
  tf_pid="$(pidof terraform)"
  kill -TERM ${tf_pid}
  wait ${tf_pid}
}

trap _term SIGTERM
...
...
...
terraform "$@"

With this approach, SIGTERM is not propagated. However, it is propagated if I call terraform this way in my script:

terraform "$@" & wait $!

Why is that?