Because he's the most complete card there is for the Junkz
Because last week were crowded with Huracan, Freaks, Berzerk and such, so top players were running a lot of soa, sob. Probably the top 10 players were running Junkz based on Qubik and such. so, many top players must have voted to ban him.
I'd argue that Gibson isn't more dangerous, but just harder to beat; but that's not the point of this topic.