(Because joining a fleet of thieves with 11ty thousand members is the same as playing with randoms)
That's easy. Why play with a clan with hundreds and hundreds of members? Sea of Thieves is awesome with friends and a crew that work together. If you have a look around the SoT forum and other places, you will notice that there are some very large clans. Well, if you want to play with players that you can get to know, learn their play style and learn their schedules, you need a smaller sized clan. Sure you can join those silly and giant clans, but that is EXACTLY the same as playing with randoms. You're reading this because you want a crew. You want a well oiled machine.