I suspect with most products associated with some celebrity they are simply attaching their name to help sell the product (and get some royalty based on sales). I seriously doubt they actually design anything and more likely are just giving a cursory approval to proposals that come their way. Similarly, you see a lot of Food Network chefs with their names attached to various things at
Walmart (and perhaps other stores). I doubt they personally design each item.
I saw the segment with Marie Osmond. She doesn't sit there and draw anything as she can't draw. (Yet, I have seen other celebs who can draw and show their ideas.) Nor does Marie make the dolls or sew the clothing. They talked to her as to her vision and concept of what the dolls are to look like that she wants. There are already many prototypes out. So she picks from them, the size, the style, the look, ie. dainty porcelain and fabric and just for display, or more plastic parts and sturdier, for kids to also be able to play with, etc.
Weeks later, after they've made some mockup dolls to show her, Marie comes back, gives input, "I'd like to put this outfit on a doll with curly red hair instead." They show her swatches of different doll hair available. She might not like the expression or color eyes on one, so it gets swapped out to blue eyes to go with the blue dress she helped design. Design as in: "Can we make the dress longer with a fuller, skirt with more ruffles?" They talk about price points. "Just one tier of ruffles, not two. . . Oh! I like the idea of ruffles underneath instead. Maybe a poufy skirt like Scarlet O'Hara's southern ballgown when she is coming down the stairs, type of fullness?"
She comes back for the final meeting where they show her the finalized designs she had chosen and the dolls are all actualized and assembled.

Of course, she's oohing and aahing over all the designs, especially the one which she designed to look like the one where she and her mom went to some event for her brothers. Of course, now the viewers want that one too.
I don't know much about Curtis Stone. I do watch Rachael Ray, who has her own cookware line. I don't know if she sells on the shopping channels. But, years before she had her own line, she talked about wanting a more oval pot or pan. They take up less space on the range as she could then have a second big pot on the next range and not have them knocking into each other, as she's cooking large amounts of food.
She finally got her cookware line and it has a LOT of oval pots & pans. And when she uses them on her show, she shows how she can angle one pot in one direction and the other the other way, and they both fit on the stove.

As a petite woman, the center of gravity of being able to carry an oval pot slightly closer to her body is a plus. They also look decorative when she simply places the pot on the buffet or dinner table, on top of a couple trivets.
She also talked about making sure there is an extra handle on the other side and that it is big enough so that when one has a thick oven mitt on, the handle can still be securely gripped. Same for the knobs on the lids. So, yeah, I'm pretty sure she actually had a big part in designing a line for how she cooks and uses the items. She didn't change how she always cooks on her show to accommodate a cookware line they gave her. These items fit the way she actually cooks and how she uses them.