Well, the Council of Nicaea was first and foremost a question of power. Its goal was to impose Constantine's caesaropapism through the unification of the christian church(es) under a centralised hierarchy and dogma. This by force and anathema, thanks to Eusebius of Caesarea. As far as I remember, the bishops from the East Mediterranean (mostly Arians) were delayed by a storm. When they arrived, the decision to excommunicate them had already been made...

"Dieu se rit des hommes qui se plaignent des conséquences alors qu'ils en chérissent les causes" Jacques-Bénigne Bossuet