Giant subs have shut down before, yet Reddit never reopened them prior to June 2023. It was the coordinated action across subs that Reddit saw as a threat, not the act of closing a sub (which had never been against the rules and still isn’t). Reddit saw the protest as hijacking in the same way that other companies feel that the workers are hijacking the company when they try to unionize or strike. Only difference here is that the workers for this company are volunteers rather than paid employees.
Sure, reddit’s a private company, so they can mostly do whatever they want, but that doesn’t change the fact that these actions are unprecedented and a huge betrayal of trust, and there’s nothing wrong with people (especially those that invested a lot of time and effort into building the site into what it is today) being upset at reddit for this.