They're optimizing for quality and civility - a certain standard of intellectual and emotional maturity - rather than controversy. Vetting through personal relationships and requiring reputation risk to let someone new in is an effective way to do that. Not every platform wants or needs to be a debate club.
I think that's certainly a goal of invite systems but I don't think Lobsters really lands this. The quality of its discussion isn't much to write home about. It is much friendlier to some opinions over others but quality is not the discriminator. If you write a middling article on Rust I can guarantee you that you'll get more positive feedback than a good article on Go or on LLMs simply because of the opinion bias of the community.
