You're assuming that Verizon wants anyone outside the Verizon technical sphere to know where their network is weak - and they don't.

Verizon closely guards information about tower loading, subscriber density and tower placement.  The last item is not impossible to find, just difficult - and you'll never hear it directly from Verizon.

Verizon is acutely and constantly aware of where the load, placement, spacing and efficiency of the signal network is.  They have a vested interest in guarding that information.  You'll notice over a period of time that a call to customer service to complain about signal level or quality almost invariably results in "Oh, I'm sorry your having trouble..."  " I don't see any reports of trouble..."  "It must be your device.  Have you..."

This is not to say that Verizon is special in this regard; all the wireless providers react the same and sometimes worse (T-Mobile).