Because it dates to a time when such attacks were infeasible. GPS is very similar in that regard. Even HTTPS was uncommon back when I was in university. NASA spacecraft still communicate over unencrypted channels.
Mindsets were different then.
Mindsets were different then.
GPS originated as a military protocol and has some level of encryption and authentication, but this is not available to the general public.
USK: Galileo also has authentication available on its civilian frequencies.
Is that already available? I thought GPS L2C didn't include authentication yet.
This was a long time ago, but I distinctly remember the encrypted P(Y)-code and anti-spoofing being operative in the mid 1990s.