All of these things happen because soap operas stay on the air for decades. Six programs with a total broadcast history of over 200 years. No other program type, except for news and sports, comes even close in audience loyalty. One character's problem leads to another's, or may require the introduction of a new character. Characters exist independently of the actors playing them.
Soap opera have a different value structure than all other TV forms.
The other forms depend on a star system that won't allow for a change in the central focus of a continuing series. We know from the beginning that the main characters, the heroes, are never to be harmed or destroyed because they can never leave the show. In typical TV fashion, the characters in prime-time series are frozen at the end of each episode without memory. They will appear next week as they appeared this week. The specific content will shift, but the formula remains the same.