Is it only grad students or is there a lead researcher that asks for grants and such? I'm not a scientist myself, the ones I know are working for the governenen

Is it only grad students or is there a lead researcher that asks for grants and such? I'm not a scientist myself, the ones I know are working for the governenent or are professors. While they are not rich they are much better off than the average person. And is feeding mice plastic and then seeing if they have plastic in them a worty endeavour? It's fine because they aren't paid as well as if they were working corporate? I'm also aware that a lot of people have to tailor their doctorate work to their advisor, meaning it could very well be that no one doing this experiment was "curious" or believing that it was "important". I'm sure you know many bitter PhD's that studied things they find utterly pointless today - I had many teachers laughing at their own peer reviewed work.