To me, that suggests the possibility that there might be the need to allocate transporter frequencies in metropolitan areas, for the same basic reason that radio frequencies are allocated IRL today, in order to avoid interference.
Doing it by wire rather than by broadcast should solve that problem.
We know that transporters involve subspace fields of some kind (from The Best of Both Worlds, Part II
: "The signals are interactive across a subspace domain similar to that of a Transporter beam."), but we don't know what kind of "wire" would be required to carry a transporter beam.
For all we know, the "wire" has to have an area of more than one square centimeter, and it can carry the signal from only one pad at a time. That would be a lot of wire, man.