Read HH St. Athanasius'
De Decretis (a.k.a. On the Defense of the Nicaean Definition), if you haven't already. It will give you a sense of some of the objections people of the time had to the Nicene definition, though not all who had reservations were actual Arians (as the saint points out in the preamble to the Defense).
More generally, I would say that there is a certain prejudice towards the party that seems to have the simplest doctrine. That's understandable, right? It's 'easier' to preach one God that is a kind of monad (i.e., Islam, Rabbinic Judaism) than to preach One God in three Persons. People want a simple God they can understand, rather than a set of theological principles which elucidate (in so far as it is possible)
how we have one God Who is Three-in-One and One-in-Three. Our EO friend above is correct that the former is more directly relatable to people's own experience of what it is to be fathers than the latter is (though I disagree that it is hard to reconcile Trinitarianism with monotheism; that's precisely what our common father HH St. Athanasius the Apostolic and others did in defeating Arianism and other soul-destroying heresies).
Recall, e.g., how even our Lord's own disciples could not take His hard sayings (such that many left Him), and said that He spoke often in parables which were not immediately understandable. And the other Jews likewise said to Him "If you are the Christ, tell us plainly."
Arianism is certainly more plain, but not any more true for it.
