From what I've heard from tech writers, it's a job that very few people want to do for a long time, or make a career of it. You get someone for a year or two at most, and then they move on to something more interesting, is the impression I have.
If you're a decent tech writer who can write well, grok engineer speak, collaborate well with engineers during crunch time before a release, and apply your technical knowledge to build and maintain documentation infrastructure... well, you'll get comped slightly beneath the level of a developer with similar experience.
For folks like me who enjoy the writing side of things, it's worth it. But there are very few people who truly appreciate both the writing and the development side of the role. You honestly need both.
Most companies pay poorly, and wind up hiring non-technical folks who can barely manage a CMS. Those people can be helpful in a larger org, but at the end of the day, most technical orgs need a truly technical writer who can talk with the engineers directly and mess around with the product pre-release.
In fact, many fields actually require their technical writers to have some amount of education in the field (e.g. biology BAs minimum or such for medical technical writing).
Unfortunately, this is a braid field in which other technical writers are performing really basic tasks, like writing straightforward gui instructions. I think this wide range gives the market an excuse to undervalue the discipline, while many writers doing important conceptual writing work are some of the most valuable participants in the arena. After all, nearly all of human epistemic and technological development has been conveyed through the medium of text. What are mathematicians if not amazing technical communicators?