This looks like more of a math problem than anything else.
If there are 1000 people surveyed and 725 of them like something, then of course that's a majority. The majority of the 1000 followers are, in this case, female, if we are only
looking at followers of this issue.
If Instagram has a total of, say, 10,000 members and 725 of them are female, then all of them are following this particular issue. But if there are 7,250 female people on Instagram, then, while they are dominating the follower count for this particular issue, it's not a majority of them on the platform.
What I am saying is, the skewed gender ratio isn't exactly indicative of nobody male being interested. It could be that lots of male people are interested, but males overall are a small percentage of the overall user base.
And if that's right, then the conclusion that you can draw isn't a lack of male interest in the issue. It would, instead, be a lack of male interest in Instagram
You also need to understand that one issue is not an adequate sample size. And popularity on any social platform is driven by more than interest. It's also algorithm and optimized search driven. 99% of Instagram could be interested in any given topic, but if it can't be found, then no one will follow it.
Other demographics could also be skewing things. Are males on Instagram, as a whole, older than females? Better educated? Whiter? More likely to be Catholic? Lithuanian?
Finally, not everyone embraces every single cause out there. And messaging doesn't reach everyone the same way. There's not necessarily anything indicating a lack of male interest.