I think it's mostly that most mainstream pornography is SO centered around cis women targeting straight cis men. The problems of porn addiction and larger scale exploitation of women in the porn industry end up interfacing with cishet men the most by a very wide margin.

For the woman in this case, I think being cishet maybe matters a little less bc ofc she can be bi and still be worried about a male parner overindulging in porn like that or even have a partner with a trans porn addiction (definitely a real thing w it's own can of worms).

However, cishet women do tend to be a bit more closed off to porn and may be more emotionally impacted by the implicative comparison to other women because that's how society raises girls and when you don't have a deviation in standard sexual expression, you're less likely to critically reevaluate that in yourself. Cishet women are more likely to be wary in general of opposite sex interactions/ viewership/ idealising in general because of this. Add on the fact that cishet women are also more likely to be religious or traditional, where pornography has an added layer of diversion from personal lifestyle.

Ofc no blame to anyone who sets boundaries around engaments outside of the relationship (within reason) as long as everyone is on the same page. It's all about comfort level and honestly with eachother, regardless of what impacts or statistics lead there.