It discourages potential lawsuits. If companies retaliate by banning entire law firms from accessing popular venues, that's going to discourage people from filing otherwise meritorious lawsuits against the venues. The difference between MSG and your house or your land is that the Nicks don't play at your house.

Just so you are aware, 'rayiner' is a pretty well known bad-actor on this site, for what it's worth. They openly discuss how they support policies based on the goal of hurting Americans they don't like, and have a demonstrated pattern of obnoxious behavior intended to frustrate. You are unlikely to actually have a productive exchange with this person.