Yes, the cultural aspect of food is sometimes very odd.
Why shouldn't we eat custard for breakfast when porridge is a breakfast dish? There is not a great deal of difference in what the contain or how they are made, after all.
What is served at the various meals has changed through history, and differs from country to country. In most European countries people would have a fit at the thought of eating kippers for breakfast, but it was quite common in Scotland when I was a child.
When I moved to Denmark, I found it hard to accustom myself to soup being served as a main dish at dinner, which is quite usual here.