I’m not going to explain how, but this isn’t correct. Most (probably not all) do it in such a way that they don’t miss any benefits.
The reason pirate teams are often mostly empty is because most of the players only join for a short bit and leave.
In an ideal world the trade off you mentioned would be real, and it would be substantial enough nobody would ever make a choice to go without their rewards.
But the game has many less than ideal situations like this. Hopefully over time they all make incremental improvements for the better.
I personally utilize a well known pirate team for a few of my alts to get invader runs when they aren’t needed elsewhere. The battle reports are extremely telling as to what’s going on with the players who join.