why?
For the same reason that one might block ads or cookies, of course. I don't want a third party corporation profiling the bluetooth devices in my house and selling data about me to advertizers.
what does their device locator service have to do with your home network?
Apple's device locator service uses the internet to report device IDs and GPS coords to Apple.
I'm genuinely curious, because nothing from that service has anything to do with anything that might happen on your network
Ideally, that would be true. But device locators necessarily report their snooping using an internet connection, and if they're on my home network when they do it then they'd associate my IP address with my location. That's way more of my personal information than I want Apple to have.
Not much I can do about that, but I can at least keep them off my network so that info isn't associated with my IP address and sold off to whoever wants it.