The short answer is "Fuck knows".
DD was a wonderful eater, ate everything we gave to her, would turn down chocolate in favour of a piece of fruit, would try anything and anything and had no real interest in unhealthy beige food.
"What marvellous parents we are", we said to each other as we patted each other on the back, marvelling at how we'd got it so right, and not having a clue how we'd done it.
And then at age 5 DD turned into the pickiest, most unadventurous eater, almost overnight. Foods that she'd eaten for years disgusted her, and the beige called to her. As she got older and the childrens menu no longer tempted her, eating out became a nightmare. Even a Margherita pizza, her favourite might have a leaf of basil or some other herb on it.
She's now 16, and thankfully she's coming out the other side of it. She tries new things, her list of options has ballooned again.
I don't know where we went right initially, and I don't know how we then went wrong. I think this most recent change is down to peer pressure, it certainly isn't down to us.
So once again, "Fuck knows."