Looking at 1e and 2e, they weren't overly sexist per se. They didn't treat women as secondary or inferior so much as forgot women even existed half the time. (Which is a whole other type of sexism.)
I think 2nd ed's use of the masculine pronoun exclusively is overtly sexist.
I also think it's more significant than the STR caps in AD&D. Caps are a mechanical element that is easily ignored (just as many people ignored the racial level caps); the language used by the authors of the game to speak to their audience is (in my view) a far bigger signal as to whether or not certain people are expected to be members of that audience.
But 1st ed AD&d is also sexist - besides the STR caps, for instance, there's the notorious harlot table in the DMG. Other examples could be given without leaving the core books, but that's probably enough.
D&D and how it approaches sex and gender over the last 35 years
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There are also restrictions on female characters (no restrictions for male characters). If you are a woman and sitting down to play some 1e AD&D and rolled an 18 for your strength your options are limited to human and half-orc. No dwarf, elf, gnome, etc. for you. And if you play a fighter you will be penalized on your bonus strength roll.
I think the better description of the situation would be this: if you roll 18 for STR and want to play a woman dwarf, elf, halfing or gnome you have to reduce that STR score. You're not prohibited from playing such a character.
And it's still not true to say that a human or half-orc woman fighter has a penalty on the percentile STR roll. Rather, there's a cap.
I take it you are also now agreeing that there was never a rule that PCs had to be the same sex/gender as their player.
It should be noted that this edition of D&D spends a lot more space than others on character background and personality.
Thereby continuing a trend - the 4e PHB had much more space on those topics than any earlier edition.
A distinction is made between sex and gender and there is a mention of sexual orientation as something to consider in character creation. The player is also now allowed to make a genderqueer or non-gendered character. The simplicity of the part regarding sexual orientation allows for asexual characters too.
I don't know in what way you think that players of earlier editions were forbidden to make non-gendered, genderqueer, intersex and/or asexual PCs.
It is true that, unlike 5e, the rules didn't mention these possibilities. But they certainly didn't forbid them.
You don't think being inclusive has impacted sales of 5e? I don't think it is the only factor, but I do think it is a major one.
It is really very hard to speculate about this without detailed sales and market information.
Did the 4e halflings - the most "inclusive" presentation I can think of ever of a PC race in a D&D edition - have a significant impact on sales to players of colour? I think speculation is next to impossible here - apart from anything else, many minority consumers of culture are relatively accustomed/resigned to purchasing products that assume a normal other than them.
