Main reason is indeed that ti looks like a ripoff of Super smash brothers.
But, if you look at SEGA, they made a sucessful kart game alongside Mario Kart.
The main issue is Sony's characters arent suficciently iconic and family friendly to make a game like this work. Its exactly the same reason why mod nation racers and LBP Karting didnt work aswell. Certain games require a background of iconic characters, and Sony is trying to make omeletes without eggs.
If they really want a game like this to suceed they have to make more platformers/adventure games that are family friendly. If you thought about this game with a started line-up of Jak and Daxter, Spike, Sly, Sack boy, Iota, Spyro, Crash, Ratchet and clank... you can see that a more consistant game is built. Sony's big mistake was also selling some of those IP's and thinking they wouldnt need them anymore (Crash and spyro). The mix of cartoonish and famaily friendly characters with realistic and mature characters obviously fails and confuses the consumers, on top of it looking like a bad knock-off of SSB.
In a way Sony did well firing Superbot. The mistake was made in the marketing and design, and not as much in the advertisement like the OP says. I know people have a hard time separating the two concepts and i honestly gave up on trying to explain. The advertisement was ok, it just had the problem that replicated from the game wich is the mix of 2 types of characters that dont mesh well together.










