This is a genuine question. I don't know the answer and my opinion is only based on my experiences.
My 3 dcs all went through the "normal" fussy phase as toddlers, when they only wanted to eat about 6 different foods. It was really annoying to be putting meals in the bin all the time but we consistently kept offering all the different foods and eventually they have come out of it and now all eat pretty well.
While my own dcs were not fussy in an extreme way, I've read threads on here and seen some friends in RL struggling with extreme fussy eaters. I think most of them would say that this is just the way they are, could be genetic sensitive palate etc...would you agree? Although I found that being quite strict and consistent about meals with my own dcs did work in the long run, I know this is only my own experience and I would not judge someone else's situation.
However....
We do not live in UK and I currently volunteer in an orphanage. The many toddlers in there are spoon-fed the same food day in day out (a sort of mushed casserole of meat, veg and crumbled bread). They just eat. All of it. It must be so boring for them but they eat because they are hungry. There isn't a hint of fussy eating, and not even the typical spoon-grabbing or head-turning thing that all my dcs did.
Surely if fussy eaters were born that way we would see at least a bit of it in there?