Quote from Yukinoshita»
prob because the only people watching Gintama° are dedicated fans.
Yep, that's why sequels on MAL have better ratings than their predecessors on average, which leads to niche shows with billions of sequels like Gintama and Hajime no Ippo to unintentionally game the ratings system and appear way above where they otherwise would. If you didn't like the first season of Gintama, chances are you're not going to still be around watching the 4th season. Ratings for long-running shows (including Gintama's original 201-episode run) are positively skewed as well, because of the 1/5 rule. If you don't like a long-running show, then you're likely to drop it before watching 1/5 of its episodes, in which case your score won't be counted.