It's tradition, It's culture.
Culture and tradition are not always moral.
Traditionally people used to own slaves. Traditionally women had less rights than men. Sometimes people cherry pick parts of history, traditions and culture to suit their actions and support their arguments. But all these areas need to be questioned and do evolve with time.
In some parts of the word it's cultural to eat cats, dogs and dolphins. In other culture humans eat each other.
Culture doesn't have to control our actions. If you have the opportunity to be Vegan, you should be Vegan. Next time you are out buying food you have the option to go for the more compassionate and more kind option, choose the Vegan options.