Symptom:
VMware NSX Federation
This is an expected behavior as per NSX design.
As per NSX-T Data Center Administration Guide, section Add a Tier-0 Gateway from Global Manager:
Note: The flag 'Enabled on Secondary' is present in GM UI since federation released in 3.0 and you can only see this flag if you have primary and secondary location configured on T0. This flag will not be visible if you have only one location configured.