Why does Gotenks wear the same clothes as Majin Boo?

[FreezaSama]

Is the outfit created from the mind of Goten & Trunks? If so, was Majin Boo's outfit the only thing that Goten & Trunks could think of?

[Savage68]

Gotenks wears the standard Metamorian clothing as all fusion warriors do; the baggy white pants is an unrelated parallel between him and Buu. Come to think of it, Fat Buu didn't really wear pants. What he wore looked more like a ... diaper. The vests are totally different, too; Buu's is more traditional and genie-like while Gotenks' is sort of puffy and, if I may add, stylish.

[Bussani]

Like Savage said:

Fusion
First Appearance: Chapter 469
Category: special
People: Trunks & Goten
Special Characteristics: The specialty technique of the people of Planet Metamor. Goku learned this art from some people from Planet Metamor who he met in the afterlife. It is an art where two humans can merge together only if their power and body size are very close, and through merging the two users give birth to a separate person who possesses power and techniques far surpassing what they had on their own. When merging, the two users must perform the Fusion pose symmetrically; this pose if very embarrassing for two adults to perform. In the story, Trunks and Goten perform this Fusion, but they fail two times because their pose is slightly wrong. When they fail at this technique, it greatly changes the body type of the resulting person, making them fat or thin, and rather than strengthening the two users, it makes them weaker. The name after merging becomes a combination of the two users’ respective names, and in Trunks and Goten’s case, they ended up named Gotenks. Furthermore, after merging, their clothes are those of the citizens of Planet Metamor. (Daizenshuu 2, p.118/Daizenshuu 4, p.116)

[Turtle Marked Stone]

Fat Buu didn't really wear pants. What he wore looked more like a ... diaper.

Hersey! They were just really poofy. Poofy pants for a poofy guy.