It seems to follow from the sceptics idea that "all isms are bad", likely influenced by the fact that most isms are in fact hideous package deals or the result of actual cult like behavior around some figure head that themselves did not even intend to create the ideology in question. Such as "Marx-ism" or "Kantian-ism", both relating to a person and their ideas taken to new (pseudo)logical end points.
In the beginning, I too was shy to use the terms themselves. "Selfish" seemed harsh, but "egoist" a little easier on my mind somehow. "Objectivism" sounded like a dogmatic doctrine, but modern philosophy in the Aristotelian tradition sounded better. It came down to having swallowed a bunch of package deals around what terms were meant to imply and in a sense holding an intrincisist view of terminology.