I can't talk for everyone but as far as I know people that search for "straight" content don't use the "straight" word in their searches, as most content is already straight. So you just need to search for whatever kink that goes with you and ignore the few gay/lesbian content that is included in the result of the search
Ah, but the searches that tally higher than "lesbian" among men, with the exception of "anal" (not a singularly straight act itself), are all related to age or race, not sexual acts that can be performed by a straight couple. That is significant, because of the hits that one tends to get when searching those categories. Namely, they return quite a lot of solo porn--women and men by themselves with no on-camera sexual partner. When a person searches for "teen" or "mature" without also a "straight," "vaginal," or "blowjob" tag he is not necessarily concerned that the star of the video be engaged in straight sex or gay sex or no sex at all. Rather, he is concerned that the star has particular qualities. A "MILF" alone in a room with a vibrator will do just fine.
The porn industry determined a long time ago that, even when the target audience is straight, the male porn actors really do not matter. It is the girl that they pay to see, and it is just as well if she is alone on camera or with another girl. It's why male porn actors get paid next to nothing unless they are gay. It's also why camwhoring is so incredibly popular.