Galileo offers cryptographic protection (OSNMA) of their positioning data. So not spoofable. For free.

Any insight as to why newer GPS satellites do not offer similar capabilities?

The GPS project began in 1973. Digital signatures were invented in 1976. I'm guessing adding it on after the fact would have been very expensive.

There have been progressive improvements as new satellites are brought into service, and those end of life retired. Perhaps backwards compatibility?

https://en.wikipedia.org/wiki/GPS_signals#Legacy_GPS_signals

https://en.wikipedia.org/wiki/GPS_signals#Modernization_and_...

Link for reference: https://www.gsc-europa.eu/galileo/services/galileo-open-serv...

Recent news: https://www.euspa.europa.eu/newsroom-events/news/galileo-get...

Not quite unspoofable, at least once the signal has been received for time-delayed rebroadcasting/meaconing.

But spoofing does become detectable by any receiver with a sufficiently accurate clock (I think for complete protection it would have to be an atomic clock though).

So until the new satellites are deployed and all receivers are replaced (say a decade or so), all civilian GPS could be jammed, shutting down a lot of civilization. Sure the military missiles will hit their targets, but nothing else will work. It would be like trying to fly near Ukraine right now where large holes in GPS appear frequently, but instead happening across the world. There are indeed very large civilian consequences to current GPS vulnerabilities, regardless of what Lockheed says. And many military systems eventually rely on the civilian world for long term support.

https://gpsjam.org/

https://www.flightradar24.com/data/gps-jamming