Hey Captain,
This is actually a good question. I guess it would be because players find a ship type they like and stick with it. I personally have played the majority of my games in BBs. I do suggest to newer players that don't have as many games invested to try out different lines as soon as they can. Remember the first few hundred battles (example) are you learning how to play the game (I hope). This time can of course vary for players, there are some that can pick it right up after a few hundred and some that are still learning after a thousand(s).
Note: IF you have been playing this game from the beginning, you can still learn new things! I still am and an constantly surprised by things =).
I have recently taken to playing cruisers a lot more and find them to be a blast! I would definitely suggest trying different ship types and this will honestly help your understanding of the game. The overall depth of the game and technical parts of the game are deep. Learn the other types of ships strengths and weakness, this will help you combat them on the water when you run into them!