Why do the same bans often occur in ranked play at Bronze and Silver ELO?

I've noticed that in Bronze and Silver ELO (Specifically 1100-1400), certain champions are almost always banned. These include

• Amumu [tank]
• Malphite [tank]
• Shen [tank]
• Blitzcrank

and sometimes

• Singed [tank]
• Darius
• Diana
• Katarina
• Morgana

Why is it that these champions are more likely to be banned than others? Also, why are tanks often banned in ranked play? I don't believe it's because the champion is overpowered.

This thread may be closed, due to Why are characters banned in tournament play for DotA-likes? but I really want to be more specific right now.

Also, these bans aren't very common in professional level play, so why are these champions so often banned at the 1100-1400 ELO? Please note I'm talking about a specific ELO so the answer would be different than the link above.