You’ve been misinformed. No “gospels” were “discarded” at Nicaea. The council didn’t address the canon of Scripture; it concerned itself with rejecting Arianism (the belief that Jesus was a lesser god than the Father) and setting the date of Easter.
there are many opinions about what happened 1700 years ago. Suffice it say that Constantine was looking for a nice clean agreeable church to start his Holy Roman Empire. The fact that babies were thrown out with the bath water is, to me, a distinct possibility.