PLBs are great and definitely better than not carrying any emergency communications device at all, but they can ultimately only send out a binary signal: "I need help at location x/y".

There's a lot of situations in which I'd appreciate being able to call help without possibly triggering an expensive helicopter SAR operation, when sending a park ranger would be more than sufficient (e.g. a sprained ankle a mile off the trailhead when solo hiking).

Another advantage of two-way communicators is being able to get instructions from the SAR team: It can be vital to know whether you should e.g. go to higher ground (because your signal has not been received yet) or conversely seek shelter from the elements for a couple of hours. Newer PLBs partially solve that problem though, thanks to Galileo's "blue light" return channel.