If you want your writing to be taken as establishing facts, you need to base it on a priori established facts; if you base it on hypotheses and beliefs then you're just expanding on the hypothesis, contributing further belief.
I suspect though that it's not the author's beliefs, just an ambiguously written way of saying that it was done by those people with that belief - in the same way that an atheist or follower of some other religion may say that Christians pray in order to communicate their wishes to God. Of course there is the rude and angry for no clear reason brand of atheist who could never bring themselves to say such a thing, but to the rest of us there is no problem in describing someone else's actions by their own reasons for doing them, even if we don't share that motivation. I have colleagues who run for pleasure; though I do not for mine.
Do other philosophical positions, like atheism or panpsychism?