I think that, just like today, it was probably customary.
Now, Jesus was called “rabbi”, but that seems to have been a title of respect and not a formal job title. He wasn’t, for example, attached to a particular synagogue, and he didn’t receive formal training under other rabbis, as would have been the custom. So, I don’t think it would be surprising if he didn’t conform to the customs of rabbis in other ways.
I have seen articles that imply that He was trained by rabbis and scholars. We know so little about His childhood and even adulthood until He started His ministry, don’t we?