A common expectation is that the GM presents adventures the players are intended to experience themselves
Many TTRPGs are played as a form of fantasy fulfillment, and for many players in many game systems that can be about being a character that is powerful, effective, and free to do things themselves. If you are presented with an important goal, it can be very exciting to throw your character into the effort to accomplish that goal and test their skills, abilities, and cleverness against obstacles. It is a very different situation to be presented with a goal and dictate that "someone else will take care of it", never seeing those events actually play out at the table. Paraphrasing an ancient koan: if an obstacle is presented but the players never really interact with it, did that obstacle even exist?
In my experience a lot of the presumed progression in TTRPGs is that the PCs will take on larger and more important adventuring tasks as they grow more powerful. The PCs do the same kinds of things, but the stakes are higher and the challenges greater. If the GM presents a quest (or similar, depending on specific game system), it's not unreasonable for players to presume that the GM is describing a task they are expected to deal with. If NPC delegates are a fundamental part of the underlying game system that impression may be different, but I don't have much experience running games in such systems.
Making it clearer why delegation is favorable may help
In the classic TTRPG tradition of "things are always clearer to the GM than they are to the players", it might help to include the narrative equivalent of flashing neon signs which indicate that this task is too boring or unimportant for the PCs to deal with themselves. I've done this with a two-fold approach:
- Express that the tasks which need to be done may not be suited to the
PCs themselves, and
- Make clear that NPCs (individual or organizations) exist which can do
Following those two tracks indicates that there is something to be done but also discourages players from doing it themselves (unless they really want to, which does happen sometimes).
I also sometimes add a third element:
- The PCs' time is better spent doing other tasks
There are things that only the PCs can do-- that's why they're such important figures! Eventually rat-catching is simply not worth their effort. None of this stops PCs from pursuing in-game activities they want to do, but that's more of a player-driven plot change to the game.
Giving the PCs a way to interact with the NPCs keeps the delegated work relevant to the game
Some games have explicit rules for this and others don't. If giving a task to NPCs means everything related to that task is over, the task may seem so unimportant that it wasn't even worth bringing up. But if you want players to interact with in-game things, methods to do that are really helpful.
Just having soldiers on the ship is not a system, nor even a clear resource for the players to direct. Some kind of guideline for maintaining and deploying the soldiers, plus potential rewards and penalties for using the soldiers to deal with problems creates game elements-- things the players get to play! It is important to use delegation as a way to make the game richer, not to explicitly remove PCs from content that seems like it might be interesting and require their attention.
An example from my experience
In one of my games (without clear rules or systems promoting delegation to NPCs) my players were interested in cultivating a new resource for themselves: a fighting gym (largely a front) from which they could recruit competent bodyguards and soldiers-for-hire. I made clear that this was possible but that running it themselves would change the tone of the game into more of a management simulation.
Running the gym would require PCs to dedicate some portion of their time to doing the gym's accounting, processing HR paperwork, dealing with licenses and regulations, and so on. None of the PCs were specialized in running businesses, so doing these things themselves would be time consuming and possibly introduce complications (bad accounting leads to extra scrutiny, which is not great for a front!).
But by finding an NPC to handle the business they could get what they wanted more effectively and with less of an investment of their personal time. This also kept the gym as a game element for them-- they could interact with it however they wanted, but had a primary point of contact they could use to get any information they wanted about the business, or to direct to make changes they wanted. The NPC sorted out the details.
At the same time I tried to use the gym to create content that was suitable for the players. Their gym became a place where complications that the NPC couldn't deal with on his own came up, requiring the PCs to intervene or lose some of the benefits the gym was providing to them.
So the gym provided benefits that mattered to the players, the NPC handled the grunt work of managing it, but the gym still provided content for the players to experience. But ultimately, if the players really wanted to run the gym directly, then it would not have been a good candidate for delegation to an NPC. Delegation is for things the players don't want to do, not necessarily a set piece in the narrative of the game: if you offer players choices, they should have more than one option to choose from.