Why don't women find happy men attractive?

I was chatting to a friend of mine at work and out of the blue she said to me "You know, you'd get loads of women if you weren't so happy all of the time."
I asked her about it, but she couldn't really explain why.

Now I've been told by so many people that I'm probably the happiest person they know and I agree that I'm a pretty happy person.
And after thinking about it, she might be right. At least it matches my experiences. When I were 19-21, I went through a flirty stage in my life and I acted super calm and chilled out in every circumstance and while I didn't get loads of women, I did have a few girlfriends and they were REALLY pretty. But I stopped doing that because it was all an act and I was tired of it. I'm 24 now and I kind of feel like I grew up since then and I want to go out and enjoy life and experience new things. Since then I've become so much more interesting and I feel like the best version of myself and as a consequence I've been so happy. But I'm also getting absolutely no attention from women. None at all, not an exaggeration.
So what she said rings true.
I also just did a google search on it and studies say that happy men are seen as significantly less attractive. Even moody men and angry men are more attractive apparently.

Now I'm not going to change. If women don't like me being happy, they don't like me. I don't care, I'm patient enough to find someone I like that likes me without putting on a show like I did before.
But I am curious. Why?