Let's see. I was 22, and I asked someone to marry me. (Error 1) Later, I did it again (Error 2)
Then, my 2nd wife's relative asked her to shoot the event, she agreed, then told me I would be 'helping' and that the work would be a 'gift.'
Even though we were relatives, they sat us apart from everyone else and fed us last.
Fortunately, the bride is so preoccupied and self-absorbed that she never complained and never asked for prints (just copied to FB), and the groom is very busy looking busy looking for a j-o-b, so he never cared. Relatives, I gave instructions on download and directions to Walmart.
So as for photography, that was my first, last, and only wedding event I will ever shoot.
I bet you find people who started out knew someone getting married or moved into weddings from a related field via existing contacts. e.g. they shot seniors, senior eventually gets married.... they shot sports, kids eventually get married....