I think this is a fundamental truth that cuts through much of the chaff. Using gender-neutral (and therefore gender-irrelevant) terminology costs nothing, so the cost-to-benefit is nought-to-something-greater-than-nought.
Yes. (And thank you.)
To always write of the player as male suggests, to some at least, that the author thinks of the hobby (perhaps unconsciously) as a boys’ club, which can be off-putting to a subset of readers – including some of us male readers for whatever that may be worth. (And by “off-putting” I mean potentially putting us off the hobby as a whole, not just the book or its author, because the author may well be taken as representative of much of the greater hobby community).
Ultimately, which is the more professional thing to do? To write of the players as men, or to write of them more generally as people?
Given that we expect a reasonable degree of professionalism from a rules author in practically all other respects (proper grammar, inoffensive attitude, instructive presentation of the rules, avoidance of overly much slang, avoidance of partisanship vis-a-vis “contested history”, etc), why not this one?