The part where you get left out is when someone from your squad sees a cool event and decides to go. They're going regardless of who else is going, but it would be nice to have some friends there.
So they post in the squad group chat "Hey I'm going to this event, anyone in?" aaaaand that's about it as far as organization goes. If you're in you're in, if you're not, that's fine too.
Not every event warrants personally inviting everyone you'd like to see there. Personally inviting people is for small primarily gatherings, not for more casual larger stuff.