All those GNSS systems use the same frequencies that can easily be jammed:

* https://gssc.esa.int/navipedia/index.php/GNSS_signal

Even the US government themselves recognizes the importance of resiliency:

* https://insidegnss.com/dot-report-on-backup-pnt-technologies...

* https://www.transportation.gov/briefing-room/us-dot-releases...