I've worked out the problem going on at the moment.
What the writers are doing is introducing storylines, and the characters for the storyline they have written.
But have forgotten to actually "write" the character. So they aren't being developed into real people living their life. And they also don't have a plan for the character beyond the storyline they are introduced for.
They should be doing it the other way around. Introducing characters, building them, developing them and then bringing storylines through naturally for them.