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.
S4 was less of a mess than S3, and the worst parts of S4 were the cleanup from S3 — namely, the Hopper/Russia plot.
S4 could have leaned much more into the “Satanic Panic” theme. Dig into the “spiritual warfare” literature of the period — Frank Peretti’s This Present Darkness (1986) or the Mike Warnke “Satan Seller” scandal (exposed in 1985).