It's a cultural convention. Physicists are not rewarded for manufacturing things, they are rewarded for discovering things. So even if the process resembles m

It's a cultural convention. Physicists are not rewarded for manufacturing things, they are rewarded for discovering things. So even if the process resembles manufacturing, they call it a discovery so they can publish a paper. Alternatively, you could say that "discovering a new isotope" is shorthand for "discovering the process by which a new isotope can be produced".