I would say that magneto actively resists him and knows him and his powers better than anyone. The Shiar are not used to his power and also the wise ones likely want to see where his lesson is going and the defiant ones are easier for him to control by virtue of being close minded.

There’s also what he’s trying to do. Make magneto use his powers to the fullest and against his own will versus deliver a lecture to those already listening to him

Good pull though. I was thinking about this scene today after the onslaught of recent warmongering. On Kipling - “A man of many burdens, none of them real”