Based on my experiences in Australia, bonuses are not merit based but essentially based on how well you get along with your boss. They can make all your hard work and outcomes achieved throughout the year meaningless. They dictate your year end review and also what salary increase and bonus to put forward for you.
I think they also play favourites as in a way they have a certain budget to work with for the team. Give more to brown nosers and less to associates they don’t like.
Lesson - at a company like this, it’s not about producing grade A product and being a grade A colleague. It’s about kissing A.