Modern ships have fewer crew members than older ships yet have vastly increased capacity. It is because they are highly automated and high tech. Navies have gone from floating steam engines with cannons to operating missiles, radar systems, drones and all sorts of tech handled by a relatively small crew.

There is no longer a need for people to shovel coal into an engine, instead they need people who can manage a 50 million dollar subsystem and keep it running for months even under war conditions. Modern militaries require bright people. They are being squeezed from two sides, diversity hires that shouldn't be there and that people who are smart enough to operate a modern ship engine or an electronic warfare system are smart enough to get a better paying job in the civilian world. When pretty much any guy who is reasonably smart can become a webdeveloper it is difficult to find people who want to spend most of their career on a ship. Some will sign up for a four year adventure, but many will drop out when they get a family and when going on another deployment stops being exciting.