I think it's very common that people read, but don't write and there's nothing sad about it. Not everyone feels the desire to write or has the aptitude to write, but that doesn't mean they shouldn't read for enjoyment, work, or education. As a writer, I love that people who aren't inspired to be writers read. If they didn't, I'd just be out of a job and talking to myself via the keyboard most of the time instead of communicating with people via writing.
If your problem is that people who write on HubPages don't read every single hub on HubPages, that's a bit odd, in my opinion. I read topics I enjoy or need for work or life. I don't have time to read things that I don't enjoy or that don't apply to my work or life needs. It's not practical to try to find all of that on HubPages, because, on many topics that fit my wants and needs, I've already read all that HubPages has to offer on those subjects.
I'm an avid reader with disabilities that leave me bedridden several to most days per week. I consume a lot of written material, usually at least two to three novels worth or their word count equivalent each day I'm too sick to leave my bed. Why would I seek out topics I don't enjoy, often written by amateurs or professionals whose styles I don't enjoy, when my need and desire is to distract myself from severe pain, weakness, dizziness, and nausea? There's a whole Internet out there with plenty of material on the topics I enjoy and need for work and life, so why should I stick to just HubPages?
Or is it the phenomenon of writers who hate reading in general that you find sad? I find that sad, too. It's like hating music and forcing ones' self to compose music or hating paintings and forcing one's self to paint. I really can't understand anyone choosing a creative pursuit in which they don't even like the finished product.