Right now commends are worthless so of course it is more rewarding. The point is that by adding value to good behavior, and especially behavior good enough to encourage other players to recognize it, the overall toxicity of DotA will be reduced.

Other games have similar systems, and it works fine. Starting with the assumption that toxic players will ruin it would mean that there is no point to making multiplayer game at all.

Rewarding good behavior, while still allowing very bad behavior to be punished allows for the game to push from both directions. There is no concrete value to the player just for reporting all the time, they gain nothing, and if they are just marking a player as Toxic they would never even get a confirmation that any action had been taken against that player. Instead, if they tried to make the game more fun and welcoming they would have the opportunity to earn extra rewards.