Why not? People are busy. They have jobs and partners and pets and sometimes kids. All of that takes time and attention.
These days I talk less to my closest friends than I did to my farthest acquaintances in high school or even college. It's kinda sad but that's just how it is. And trying to get together face-to-face? LoL, it can take months to align our schedules.
And when it comes to larger stuff. Sometimes you just wanna organize a birthday party or something for everyone, you know? If I want to invite you to a party like that, are we not friends?