My best female friendship works precisely because there's exactly zero sexual tension between us. We talk about gardening, cooking, our respective childhoods, how many times she's almost gotten killed by people she was sure was gonna kill her but she wasn't going to stick around to find out.
Guys and girls that say this aren't really interested in friendship, period. They don't become friends with people of the gender they're attracted to unless they're attracted to them. And they can't control themselves once they do. This is why they say such things.
I can be friends with someone I'm attracted to without trying to turn them into my girlfriend. I can be friends with a lady I'm not attracted to. It's that simple. If you can't, then you'll think nobody can because everyone thinks that everyone else is just like they are when it comes to these things.
What I have noticed is that attraction is a motivator to get you to spend time with someone. If I were married, I'd be way more inclined to want to spend more time with platonic friends.
But I'm not. I meet my platonic friends at the coffee shop when it's convenient for both of us. I only very rarely make such time otherwise. Because what they like to do is rarely what I want to do. So time with all my friends happens in the context off something we both like to do, coffee and conversation.
It takes more than platonic interest for me to plan to spend time with someone doing something I wouldn't ordinarily do myself.