When 𧸇 was used as a component in other characters, 𡍬 was reduced resulting in 𧶠 and then 賣. This is different than 賣 as a standalone character, which although graphically and semantically similar, has different origins.
𧸇 and 𡍬 don't sound similar in modern Mandarin due to historical phonetic changes. They were more similar in older Chinese.
