Probably because the Wilderness Protocol is not widely known and requires someone listening. While this might happen near some popular National Parks, in general you'd be better off checking the frequencies of the local repeaters in that area before heading off into the woods. There are several large, multi-state linked repeater networks that are actively monitored. Of course, their coverage may or may not work for you depending on terrain.
If you want fail resistant emergency help anywhere, buy a SPOT GPS Messenger. A unit costs about US$120
with a year of service is around US$100. These use GPS to fix your location and sends a message with your location to a service using commercial satellites. For obvious reasons, the coverage area is most of the planet. If your into the wild for more than a couple days, add a solar panel and you'd be set.
If you want to stick purely to ham radio, learn CW. A small QRP rig would run on a 9V battery for many hours. That, plus enough wire for a 40m end fed would still weight less than your typical HT. And cost far less.
If you have more weight budget, carry an FT-817. With the W4RT battery, I get 4-6 hours of operating time on SSB. And besides, you actually intent to operate while your out in the woods and have some fun.