Thats hard to say, if you only focus on the smut, you'll narrow your target fully to bi people, but yeah, as the latest Last of Us episode shows, if you make the story great, you can have same sex romance in it, and even an entire story about same sex romance.
Of course, there's gonna be some people that are gonna be turned off by it, but there always are. if you have a great plot, and introduce romance only later, people are gonna enjoy it.
My brother is completely straight, but I suggested a story to him, he read about 60 chapters of it before finding out the male MC was gay, he was taken aback, but the story was still good, and the romance wasn't forced, so he continued to enjoy the story.
What I'm trying to say is, if your story is about the sex, you're gonna turn of a lot of people, and narrow your audience by a lot. There's no use complaining about it, it's the same as if you make a ultra violent story focused entirely on guns and macho men, then complain that only a small minority of women enjoy it.
But, if there's some of it in your story, it's not such a huge problem... there's still gonna be some who won't read same sex, especialy M/M... but then again, there's some who will be there exclusively for the M/M, probably fewer people though.