I've been on a lot of cruises. Aside from sleeping, I'm pretty much never in my cabin. Doesn't really make for a good comparison to a flight.
For a certain price, you’ll find someone to do it
I've never been on one; to some one who has, how do you avoid going nuts or getting depressed after a few days?
I deployed on a sub five times in four years, so I'm maybe not the best one to give an example. For us, we got used to the 'no outside' within a day or so as there is always so much else to do.
Long term, you make friends, come up with portable hobbies, and just dig in to the job for a while.
Consume as much food and booze as possible to drown your depression caused by being crammed on a disease-ridden ship with 3,000 strangers.