For mobile phones RRLP (and its LTE descendant) has been in the GSM spec for years now.
https://en.m.wikipedia.org/wiki/Radio_resource_location_serv...
However they still ask for details because it’s more accurate and faster to ask and while they can get your location if the location is in a building with 200 apartments it doesn’t really help but denying they have the info when it’s an FCC mandate is a bit silly.
> Wireless network operators must provide the latitude and longitude of callers within 300 meters, within six minutes of a request by a PSAP. Accuracy rates must meet FCC standards on average within any given participating PSAP service area by September 11, 2012
As such the location provided by a barely-compliant mobile phone provider would only have a 50% chance (depending on distribution and what average means exactly in this context) of being within 300 meters of the actual location of the call. I don't know what the real world numbers look like, but it seems very reasonable that the emergency service personnel would need much more accurate location information than that in order to respond without a lot of searching.
I called 311 at 2am once, and had to give the address to the 911 operator because she had no data at all. This was from an AT&T phone, so it's a miracle I got through at all.
(AT&T, Verizon, and T-Mobile are all 1-bar for the 50,000 people near where I live, and they constantly complain about it on the neighborhood web sites. Only Sprint has a good signal, and that's because of old Nextel gub'mint contract towers.)
Emergency services would have your GPS coordinates these days, or at least could as its integrated into the spec.