It's an ease of use thing. Some people forget to set static IP addresses for the devices and when the device is created the DNI is based on the network address. So if the device is grabbing an IP address via DHCP, the network address might change the next go around and now the DNI is invalid and the Hubitat integration starts bombing out.
The SSDP discovery process can find the Wink Relay devices on the network via a broadcast... so even if their IP address changes, it can figure out the internal device IDs and update the DNI in Hubitat accordingly to keep things in sync and working.
Searching for that event value urn:sharptools-io:device:WinkRelay:1 in the community search would land you on the following result which explains the process and how you can disable it if you'd like: 
