It was just evolution in the game.
Once they upped the weight limit from ~80KG to 100KG you saw a lot more imaginitive robots with more destructure weapons though.
Kinetic discs basically became the favoured weapon with awesome destructive power, relatively simple to design and implement too.
Chaos 2 never really got an upgrade when the weight limit was increased, so was effectively competing against robots in a higher class... it was still one of the best robots capable of flipping things out of the ring. With an upgrade (Chaos 3?) it would have been pretty immense.
Flipper bots are ghey
