For whoever is doing the pressuring to work faster, supposedly the manager who is supposedly doing it for the benefit of the company.
I'm not saying this is better for the employee, but if you're asking "why are they pressuring me to work faster, my work is not critical" then the answer is "they still want to get as much out of you as they can, even when it's not critical".
I'm not advocating for anything, I guess the original phrasing of the question was ambiguous- I read it as "I don't know why my boss cares how fast I work if my work is not critical" and am answering that question.
But it can also be read as "why is it to my benefit to work as fast as I can?", which is apparently how you interpreted it.
I'm not saying this is better for the employee, but if you're asking "why are they pressuring me to work faster, my work is not critical" then the answer is "they still want to get as much out of you as they can, even when it's not critical".