GPS tampering “data” from a company who’s upcoming tech is advertised to solve the problem their data shows is indeed a problem, and coincidentally also raised their 170M series C
I would guess the business model is 'pay us and we'll give you the encryption key to our coded transmissions'.
Those coded transmissions are far harder to jam unless you have the key. So it's all about selling to as many customers as possible whilst having not a single customer leak the key.
That's why militaries use keys that rotate daily and won't let anyone else use the military signal.
Your satellite doesn't want to be sending out lots of different signals - due to a limited power budget.
So you have to send out one (or maybe a couple) of signals protected by a key.
Yes, you can distribute that key individually to clients using public key cryptography over the same link (and many services like pay TV do exactly that).
But fundamentally any client who is able to decrypt the main stream can also share the key with someone evil who can use that info to jam the same stream.