Others have already pointed out that these systems are also susceptible to the same types of jamming/interference.
Two other issues - the biggest one is mentioned in the article - global coverage. GLONASS is the only one to claim global coverage.
The other issue is that there's still a huge number of devices that don't support those systems. Most of the time if something says it uses/depends upon GPS, it means literally just that one system, not the others.
Two other issues - the biggest one is mentioned in the article - global coverage. GLONASS is the only one to claim global coverage.
The other issue is that there's still a huge number of devices that don't support those systems. Most of the time if something says it uses/depends upon GPS, it means literally just that one system, not the others.