Megatron knows the easiest way to control Soundwave is through those he cares about.
Specifically if he knows that Soundwave is already aware of what he did to Ravage and how much he's already brutalised and traumatised Ravage before this.

He can absolutely do it again.

DON'T WORRY!
After this Ravage was tended to by the Soundfam and was pampered by them. He survives!.