Very little in this show makes sense.
Jackie is a primary school teacher who... does no teaching (or planning, or marking). Instead she wafts around the island looking moody and doing completely random things, like turning up to funerary celebrations and ruining them. Or breathily muttering "WHY DIDN'T WE FIND HER - ALL THOSE YEARS, UNDER ALL THAT RUBBISH..."
Bull is a completely incompetent policeman who fails to follow leads, who keeps giving his ex-wife access to confidential police information and documents, who randomly decides to eat bits of plants by the roadside and/or have one night stands with gay weathermen, while ignoring:
Deng, who is a sensible and competent officer, but who inexplicably ignores all of Bull's stupidity, while being treated with total contempt by him, despite the fact that she's a way better detective.
Literally everyone in the village wants the murderer found, but they are all completely unwilling to provide any help or assistance to the police, and they all mutter in their dodgy Welsh accents about "outsideerrrs".
Each to their own, and if you are enjoying this I'm happy for you, but... in my opinion, it's a load of old shite!