Well, I think there can be many reasons why it took her this long to deny it. Some from the top of my head:
1. She wasn't really asked about that when she was in the group.
2. She's distant enough from Morning Musume. Saying anything on the subject could have affected the group's image.
3. H&A, ABCHO, whatever duo projects are long gone so no need for fanservice.
And I use the term fanservice in the sense that Yossy herself said that it was a rumor among us fans that she and Rika have something going on. They couldn't break all our hearts early on. I think people who tolerate or accept whatever relationship they were perceived to have was their principal market as a duo.
This is not the first time Yossy has denied being gay but this is the first time I heard she clearly referred to our particular fandom.
It's fantasy for a lot of us, but I also think we have to understand that they are very real people with a lot of things going on around them that we don't see or know about.
I think like that guy from Ariyoshi many of us wish that it were true. For me, it's not just because of some sexual fantasy but because they just look good together and they've done good work together.
Whatever it is they have going on and whatever they say about it, I respect that and actually I don't really mind it at all.
I hope they continue to work together and that things like this don't affect them in a bad way.