While the telco of course has the GSM tower location info, 3rd parties had to collect the info themselves. Google's army of Streetview cars built out their tower database. Mozilla's Stumbler app was used to collect theirs. All of these data brokers keep their info centrally, and map apps on your phone query them on demand.
The telcos know where you are, but there's no good reason to let 3rd parties know all the time.