That most math books I read don’t discuss it.
And maybe you should not make generalizations based on your reading list. In particular, your reading list could be selective, thereby making generalizations worthless. Or you could misread your reading list, where they do not explicitly state that they believe in and/or depend on proof by contradiction.
Returning to the discussion: adamnemecek said that most mathematicians needed to know about constructive mathematics. When asked why he thought they didn't, he said that most math books he read didn't discuss it (presumably, "it" = "constructivist mathematics"). So I said that adamnemecek couldn't draw that conclusion on that evidence, though I should perhaps have been clearer that, as you said, "99% of math books don't worry about issues like the axiom of choice or constructive math". You're actually agreeing with what I was trying to say - you can't look at an average math book and decide whether the author knows about constructivist math or not, because it's outside the topic of the book. Even if the book does lots of proof by contradiction, that only proves that the author is not writing a constructivist book, not that the author is unaware of constructivism.
I think adamnemecek wants every math book to be explicitly constructivist. That, I think, is a complete misreading on his part of how important constructivist math is.