so we've determined in another thread discussing weapon carry limit that the devs made it two for a few reasons.
https://www.seaofthieves.com/forum/topic/30946/weapon-carry-limit-edited
one is that it follows through with their idea of horizontal progressing; somebody with a more than 2 weapons to carry officially has an advantage against all new players starting with only two.
another is that it prevents cheating with macros. with a macro, a player can shoot and switch between all 4 weapons and deal a lot of burst damage.
another reason is that it forces players to utilize melee more often and play an aggressive role rather than a safe one. it also presents more risk for carrying two ranged weapons for more ammo.
another reason is that it allows players to play different roles among a crew. one can have a sniper, the other a blunderbuss, another the pistol, and so on.
another is that it makes encountering players a lot more interesting; not every player you face is going to have every weapon in their inventory, and not all of them is going to carry a sword either.
the final reason is not really a well supported one, but some people just did not like to take the time to scroll between weapons until they equip the one they need. there my be more weapon types in the game other than the 4 we have now, and if the carry limit determines on the weapon type number, that can become annoying.
it is unconfirmed that they mad the carry limit two specifically for these reasons though, it may go back to three of four if the community thinks otherwise. so far, the two carry limit has provided a lot more benefits in terms of fairness and design rather than a carry limit of more than two.