Pega RM v6.1 robot register REST API sets "pyOpAvailabiity" to false due to that heartbeat fails.
As per the OOTB activity "pxRegisterRobot" that sets "pyOpAvailabiity" to false. Corresponding step description explain as "set pyOpAvailabiity to true only if the robot is registering on it's own - not via RPA Svc registration call".
How to register a bot on it's own without calling REST API?
There are two operators created on platform one for Robot Runtime and the other for its RPA Service. So those steps are executed when a call is made to register the Robot Runtime without the RPA Service.