Why is it that when you lose in a PvP match your ranking goes down, but when you win you get no points?

On successful defense you got 0 points but the attacker lose trophy
i think it is to reduce the gap between players's ranks and make it bit hard to rank up
for example

A and B players has 10 trophy , A attacked B and lost so he lose 2 trophy and B trophy are the same so they have now 8-10 trophy

what many want is a trophy for successful defense so A lose 2 , B gain 2
the trophy will be 8-12