why does turning on your wifi on your phone, even if not connected to a wifi, help pinpoint your location.

In the background the phone is scanning for which wifi hotspots it can see around you. Given this information your phone can ask Google/Apple/etc over your mobile data connection where hotspots with these particular names are located, these companies will have large databases of such information and can tell you roughly where you are given this list of hotspots. The relative signal strength of these different networks can then be used to calculate where you are relative to all of them. Google/Apple/etc build these databases by occasionally having your phone report it's GPS coordinates along with what hotspots it can see. I think androids used to commonly do it when you put them on charge. Google also used their streetview cars to do the same thing on a slightly larger scale, recording what hotspots they could see constantly as they drove around photographing.