Season 1s are great, setup, some payoff, a bit of lead into the overarching story. Then season 2 to X. The heroes win and then lose in the final episode, cliffhanger to next season. People get bored. Final season is announced and they wrap up the show.
Couldn’t agree more. The final season was such nonsense it soured the whole show and I’ve never bothered to watch it through again (ignoring the incessant “tell not show” with being told how brilliant Sherlock is but never really showing that, and how the mysteries were never deductible by the audience).