Not everyone you've connected with on social media is actually a "friend". You connect with work colleagues and acquaintances you meet at parties and even random strangers you share one drink with at a bar that you found cute. So yeah, a lot of them aren't actually "friends" but the platform folks like calling them friends.
But you do have people they're that you've known for years and it means something to be connected. And your interactions with them on the platform mean more. And thus it hurts more when got strong negative signals from people you consider to be friends.
Blocking strangers and acquaintances is easy. One politically charged statement that goes against your values is typically good enough reason to disconnect. But it takes a lot more to disconnect from a friend. It takes way more to actually block that friend.
When you block someone who is actually a friend, you're telling them that you don't want to communicate further. Sure you can pick up the phone and call but why would you even someone has used social media to put a wall between you two?
And when a friend since your elementary school years blocks you without speaking to you, well, that's an even stronger message. And I just want to shake it off has it had been a while since then, but it still pisses me off. And I don't want to stand for bullshit like this anymore.