Ah, now I understand: When you wrote "In book publishing it's shrunk to a very small niche, even in technical areas", you mean the "technical areas" that don't

Ah, now I understand: When you wrote "In book publishing it's shrunk to a very small niche, even in technical areas", you mean the "technical areas" that don't use equations in their books. My background is blinding me to the fact that books with equations is really a small niche market. That small niche is completely dominated by LaTeX.