People have this misunderstanding, if they add ads, it will be for users of #threads, other servers will not see the ad. What about if they inject an ad to every post? That would make no sense, their income come from ads, but personalized ads, you probably hate them, but tons of people find them useful, besides they won't be able to have metrics for a wall of text or image at the bottom of every post for others in the #fediverse.