Why working with Domoticz Arduino serial mysensor GW + sensor needs extra code (sending initial values) to work in HA?

I got Arduino based serial GW with sensor which worked fine with Domoticz. Same board/fm failed (no sensors showing up) with HA. Seems code lacked sending initial values which is required in HA.
Why sending initial values is required in HA, while Domoticz seems to work without that?

Problem seems to be addressed in Presenting initial value with home sensors-node?