I walked the Invierno last year, and I have to say I'm not surprised by the statistics you cite, Laurie. For one thing, I agree with others that many who walk the Invierno probably don't get a Compostela for it. I didn't, for one.
I also agree with others that folks may be put off by the isolation and difficulty of some of the stages of the Invierno. I walked from SJPP, and left the Frances to take up the Invierno in Ponferrada, as I'd planned to do (with a printout of Laurie's extremely helpful pdf guide in hand.) Leaving the "river" of the
Camino Frances in Ponferrada, with its stream of hikers, albergues and cafes, did give me a lonely and uneasy feeling--especially on that long, solitary hike up the mountain trail on the way out of the city. That loneliness diminished as I fell into the different, quieter rhythm of the Invierno, and was finally replaced by euphoria. It's that beautiful....
I walked alone much of the three weeks I was on the Invierno, and encountered maybe ten other pilgrims in that time, one of whom was a woman I walked with for a few days, and a Dutch couple I walked with for the long stretch into Lalin (they said the Invierno was the most challenging Camino they'd done in terms of uphills, and they'd walked most of the routes in Spain.)
All the other walkers I encountered were men. I can see how women could be nervous with the isolation of parts of the Invierno--for example, there's a whole day spent walking along wind turbines, and another long (glorious) day through mountains on a remote path after Las Medulas. But objectively, it's as safe as the
Camino Frances, and probably more so since pilgrims aren't going to be targeted. The challenge is not so much the external conditions as it is managing emotions, especially managing the fear that we women have been programmed to feel when alone in an isolated place.
If you want the camaraderie of albergues and pilgrim cafes, the Invierno would be disappointing. But as others here have said, there are many inexpensive hotels and guest houses along the way, and plenty of places to eat, most serving better food than on the Frances. Everyone has a garden in rural Galicia, and that means much better salads and french fries than you get in some other regions!
I also agree with other posters that the local folks are very friendly on the Invierno. For example, I was in a village grocery store getting a few things, and thinking to myself that my backpack wasn't buying me any smiles from the proprietor or customers. As I was walked outside, the lady at the cash register came running out with a huge hunk of cake to give me, "la peregrina." Ok, maybe my eyes did tear up a little...Farther up the road in Barxa do Lor, Jose and Pacita insisted I stay another night and wouldn't accept payment for my dinner with the family, or for my second night of lodging. Asun in A Rua took me on a long driving tour around the area when i spent an extra day with her. So yes, in my experience this route is full of lovely people who are happy to see a pilgrim--though many you may encounter have never heard of the Invierno, and will tell you that you've strayed far off the Camino!
I agree it's a good idea to learn a bit of Spanish before you walk this, even a little goes a long way to help make some new friends here.
In sum--I loved the Invierno, and would walk it again in a heartbeat. And I can understand why it hasn't become a popular Camino. (But I think that's ok with me....)