If the Slave does not receieve a RSTACT CCC before seeing the Slave Reset Pattern, then it uses the default action of Peripheral Reset (i.e., reset just the I3C block). If the Slave again receives no RSTACT CCC before seeing a Slave Reset, then it then escalates to a Full-Chip Reset. It therefore holds the state after any default Peripheral Reset, so as to activate the escalation. That state is cleared if the Slave sees either an RSTACT CCC, or a GETSTATUS CCC addressed to it.
The purpose of this mechanism is to fix a broken system or setup. Because the Slave Reset Pattern Detector logic is normally separated both from the I3C block and from other parts of the main system, it will continue to work even if the rest of the chip has become broken (e.g., clocks stopped, Bus locked up, etc.). This means that not seeing a RSTACT CCC would be a symptom of a large problem, so the Slave escalates in order to recover from such a broken condition. The Slave first performs a Peripheral Reset, in case the fault condition exists only in the I3C block itself.