Look, they're bent pipes because it's faster, cheaper and more scalable. If you do authentication, you need the satellite to process and validate each packet before repeating it. That means that suddenly you need a processor - a beefy one, to handle so many signals at once and understand the modulation, and you have a delay between receiving and sending. You also have new failure modes to worry about, new components that can fail, protocol lock-in, maintenance, etc.

Bent pipes are perfect. Not everything needs to be overengineered to hell. A handful of pirates aren't a big enough deal to boil the ocean with a DSP. And assuming that the signal is Manchester-coded, you can defeat the pirates in future models with a simple analog filter to remove their noise.