This is a pretty typical state of affairs. And there seems to be no disquiet with or debate about this state of affairs -- it's simply accepted that that's how things are. When it's mentioned at all in horse magazines, it's nearly always "How can I get my significant other interested?", and doesn't address any wider issues of gender parity.
(At the highest levels of riding, the gender balance is much more even, which is of course also an interesting subject for debate.)