I guess to become a pirate you would have to reject the known laws of the military bodies who patrol the seas and cities. Also, I think that greed would be part of it since you would be stealing from normal citizens from the towns you loot. I’m not really sure what else would make someone turn to the life of being a pirate.
How do you think a pirate becomes a pirate? What do you think influences their choices to be a pirate?
They watch one piece and decide to be one
jk
As you said greed or the thought of easily becoming rich might be what leads the this. Same as becoming a theif/robber. Or maybe people think its cool hence they become one
Do you want a historical reason for it or do you want me to make up some nonsense?
I would also add probably a background that makes it that you would choose the “easier” path to make money rather than find work, so for example if you didn’t grow up knowing other means of income?
This question reminds me of two videos made by this informative youtuber
But also I don’t doubt it’s much different for why people do crime today- either out of the established system failing them or other influences such as various aspiration (Freedom and Loot) and a different morale code
How someone would actually find a way to become a pirate- my best guess is just going to shadey areas where goverment authorities are scarce and ask around- or perhaps join one after they raid your current ship
But then again, that is just speculation I have done zero research and everything I say is 90% likely to be wrong XD
The joke answer I’ll say is that they have a 
dream so they set out to sea to fulfil that dream and grab a bunch of people a long the way who also have dreams 
Tangled intensifies
I was more referencing One Piece but tangled works too 
Oh. Duh.