Anyone even remotely familiar with the criminal justice system, human psychology, or even just fucking handling a pet animal will tell you that that the most important part of the punishment is certain, swift feedback. Negative behaviors are very impulsive so in order for the brain to link the punishment to the behavior, it must be delivered relatively promptly.
The Behavior Score system is as far from this as possible. Most good/bad actions barely move the needle. Your score going up/down 50 points will hardly impact your next game at all and doesn't offer much disincentive for players seeking out catharsis from flaming or griefing teammates.
The game used to rely mostly on low priority games, temporary matchmaking bans, and frequent mutes. These are much more effective tools as they immediately signal to the player that their actions are bad. I'm not really sure why they decided to introduce behavior score rather than continue tweaking these punishments.