Competing with four free GNSS constellations is an interesting business model for sure...
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.
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.
To add to that, other people won't be able to spoof the original stream (as that needs the private key), but instead only jam it.
It would be the same failure mode as SSL certificates.
An attacker can record the streams and replay them milliseconds later.
A client can protect against this if they have an atomic clock, but that's only for clients willing to pay a decent amount.
Obviously you could have some "revoke each players keys in turn until the jamming stops" scheme, but it seems suboptimal.
I would have to look at the math more specifically, but I would think it would be impossible to both disguise the compromised key and take advantage of the key to interfere with the signal in the way its designed to prevent. And even if you did, I’m fairly sure the jamming would only affect users whose decryption runs through your branch, and in your geographic proximity so I don’t think it would have an advantage of countering the below the noise floor decryption designed to mitigate against jamming.