Why is 見 replaced with 见 from simplified to traditional Chinese?
According to the Wikipedia,
来自于行书与草书的楷书化.

[注 1] lists some examples, 许多偏旁如讠[訁]、饣[飠]、纟[糹]、钅[釒]、呙[咼]、见[見]、页[頁]、贝[貝]、车[車]、东[東]、门[門]、马[馬]等来自草书。

Some simplifications were based on popular cursive forms (草书) embodying graphic or phonetic simplifications of the traditional forms. (from the English version of the Wikipedia page)

Therefore, 见 replaces 見 because 见 is the cursive form of 見.