Mostly because he is just pushed and so people have an irrational hate for him.
Rodtang easily defeated Takeru. People hate Rodtang, so of you're saying Takeru was past his prime, which is nonsense (even if he was, it wouldn't have made a difference, it wasn't even remotely close). Same thing happened when Tenshin beat Takeru after people thought there is no way a hype job like him would win. People will always hate the big personality guys that are "pushed".
Rodtang basically beat Tenshin also. And he fought evenly with Superlek despite people saying Superlek would kill him. So Rodtang is an elite fighter, nothing fraudulent about him other than an occasional dude that doesn't watch MT saying he's the goat.
Takeru went to fight Superlek, Rodtang, and Tenshin and lost to all three of them. He fought the best guys from ONE and Rise and came out the losing side. No one screwed him over. He wanted to fight the best after ruling K1 and people found out he's not the best.