Are you sure that was the actual reason? May I suggest that the actual reason was to stop people from using the trick with the gold units to obtain multiple bonus units. I hope gree people filled you in on that. Gree doesn't care about complaints but you guys sure care about $$ and people getting bonus units they shouldn't get.
May I also predict that this new event is gonna be a huge disaster. If you guys at gree don't see it, you deserve what's coming.