Question about bad routes and "route treatments"

[Ansextra]

Route treatment is often required due to an outbound call to a particular number that fails in a variety of ways... error messages, won't ring, rings but won't connect, connects but no audio, connects then drops immediately or fairly quickly, etc.

I understand that but still don't understand why it should be necessary in the first place? It almost sounds like each number needs to be entered manually into a call manager. That would be an absurd state of affairs.