Really? Well, I guess that's a matter of space and how you see the character.
Back when I wanted to buy my first HT figure, I had to decide between WS from TWS and from CW. Ultimately I chose TWS version because it had the cooler outfit, 2 heads, tons of weapons and was how he appeared in TWS, which is my fave MCU movie. I thought, if I spent that much money on a figure, I gotta pick the one I like best, despite the price. Now, months later, after I had ordered CW Cap and a few others, I decided to order CW Bucky as well. I didn't want to get both but looking at the two figures and especially at the character in the two movies, it's just two different characters to me in a way. Displaying TWS Bucky with CW Cap kinda felt off because that's the brainwashed WS and not really Bucky yet, ya know? So since I wanted to display Cap with Bucky, there really was no other way but to get the CW version too. That one's Bucky, while the first version is WS.
To me it's not like two figures of the same character with two different outfits, it's more like two different versions of the character and it really comes down to which version of the character you prefer and whether or not they're interchangeable to you, they're not to me so I'd never think of selling one for the other. ^^ Does that make sense?