What are some of the high-priced proprietary ones?
Afaik, Adobe InDesign and Quark dominate the market, with InDesign being the de-facto standard. They're not as high-priced or numerous as they used to be, though; there were a bunch of sold-to-professionals-only packages in the 80s, but there seems to have been a convergence between desktop publishing and professional print prepress, so everyone just uses InDesign or Quark now.
My guess is it just takes far too much implementation effort to replicate (or even significantly modify) something like TeX relative to the fairly small userbase of academic-paper-writers. The low-level typesetting-related parts in particular are pretty hairy and hard to get right, so experimentation tends to happen more in higher-level macro packages.