There have been suggestions that where repeaters exist on the 675 pair, or if a new repeater is installed, that they have the 141.3 Hz tone available for travelers assistance/emergency use, but it was never mandated. Base station and mobile station units were also encouraged to monitor 675/141.3 when not otherwise actively communicating with another station on another channel/tone.
There have been suggestions that FRS users monitor ch 1 with a 67.0 Hz tone (channel 1 - tone 1) when not actively communicating with someone else for the same, but again, it was never mandated. (Use ch 1/tone 1, or better yet, ch 1/CSQ, as a "calling channel", then switch to a "working channel" to complete your communications, then switch back to ch 1 again.)
In the areas that you find them monitored, it is entirely voluntary. This may be a club/group, or just civic minded individuals.
Although I am licensed, I don't currently have a working GMRS radio. However, when I take a random roadtrip out of the Phoenix area, one of my scanners is typically scanning all of the MURS/FRS/GMRS channels in CSQ, as well as the five 49 MHz Part 15 frequencies, and the Amateur FM simplex calling channels (and an AM calling channel or two.)
If the capability doesn't currently exist in your area, why not start monitoring yourself? You don't have to be a member of REACT, or any other club/group to listen to the channels. (You can't claim REACT, et al, membership if you're not a member, but you don't have to be a member to monitor.) Even if your station only covers a few square miles simplex, that's a few square miles that would be covered, when before they weren't.
John
WPXJ598
Peoria, AZ