Because we don't know if a device that was not seen in weeks with some IP address 192.168.0.3 is still the same as it was a long time ago. Most users have routers with sequential IP address associating DHCP servers, i.e., the IP a device gets solely depends on the order of switching the devices on at this day. This makes the entire identify devices by their IP addresses idea pretty useless and is why I am still cautious with this approach.
Yes, this is because the last query of this device was three days ago, i.e., it isn't present any more in Pi-hole's memory.
edit: I pushed another small change that should finally eliminate the double addition of devices with the same IP address. This should resolve most of my concerns.
I hear you, but I don't think we want to push the release of v5.0 much longer. There has to be something left for v5.1 