Don't arm the consumer
The *real* reason for not handing over the data for fear of publication and reuse is that the paying consumer will get more information in helping make informed choices about who to hand over money to.
Imagine having access to an independent coverage map to help you decide if you can move from one crappy network to another in the four common locations you spend time in (office, home, pub, girlfriend ... whatever) ?
It's not really in the network operators interest to reveal how poor they actually are. Especially with the Nothing Nowhere consolidation going on...