I don't know why you are so surprised given this decision actually overturns a previous one that basically ruled that not only must there be some means of this communication, but that the employer can't choose what it is (Purple Communications as mentioned in the post). So at one point the rules were actually stronger than they are now.

The decision requires that there must be some way for employees to communicate and organize among themselves. Generally courts take a dim view of things like "yes you could technically do it if you broke our policies to grab people's numbers and then started a Signal group". So I don't actually agree with your interpretation of what the ruling says that employers don't have to do anything. I will also note that, while unrelated, employers must provide employees with tools to organize in the physical space (e.g. by putting up posters in common areas). Your shock at the existence of these rules is unwarranted. I would definitely not use company resources to organize if I could avoid it just because it seems like a lot of trouble that is probably not worth it, but there definitely are protections around this kind of thing.