Are cruises just about entertainment and food?
Yes, plus the ports you stop at and get to leave the ship and see the sights. Also it's a way to meet new people.
No. Most people like the shore excursions.
drinks. let's not forget drinks!
If they were, I doubt there would be many repeat cruisers. My wife was of that opinion, but I talked her into taking one with our kids, who were young at the time. When you go on a vacation with kids, you spend half your time watching them, the other half entertaining them. It isn't much of a vacation for parents. On a cruise, the kids go to the kids' programs, and they love them. So you get to relax, meet people, go to presentations on anything from Caribbean art to shipwrecks around Bermuda, etc. You get on, unpack once, and wake up in a new place most days. Even sea days are fun, as you have no where to go, and all day to get there. No driving, hunting for restaurants, dealing with cabs, etc. You just relax. We've met people from all over the US, Belgium, England, New Zealand, Australia and loads of Canadians. I travel a lot for work, and often connect with people I've met on cruises when I'm near them. We meet up with some Canadians we met cruising every year in Niagara and do wine tours. You know going in that your food is covered, and can plan ahead for any additional costs, so it's easy to stay within your budget. People who whine about water systems, noro-virus, etc have either never been on a cruise or know nothing about it. I've now been on 15, and I'm going on 3 in 2019. I also do land vacations, which also have their benefits. But for sheer relaxation, you can't beat a cruise. And heck, a week on a cruise is cheaper than a week in a decent vacation destination.
There is a lot of liquor.
No. You forgot about severe sunburns and alcohol poisoning.
No. They are also about unsafe water systems. Only drink bottled water, do not put ice in your drinks. If you drink booze, only drink 80 proof and do it neat.