>if you’re solo it seems like they expect you to buy 2 spots

Cruises are probably more complicated because they price things other than your cabin into the "experience." (Though I think the Queen Mary 2 a few years back was slightly less than 2x for just me.) But the random Marriott doesn't really care if there is one of you or two when it comes to pricing.

Why wouldn’t they care?

I imagine 2 people use roughly twice the bedding, towels, toiletries, etc., on average.

If there's two beds, maybe. If one bed, doesn't matter how many people sleep in it. Maybe twice the towels?

I'll say over the years most places do not respect the "if the towel is not on the floor don't replace it". I'm fine with reusing a towel to dry off twice, but some hotels change them every day, even when their signage is indicating a protocol to prevent that sort of waste.

2 vs 1 doesn’t significantly impact space or cleaning labor, unless you’re staying in a super minimalist itty bitty unit (which I rarely find exists anymore)

Well, they mostly don't. They're often using the same bedding. Most toiletries are squirt containers these days. I don't think toilet paper is that expensive. And another towel or two to wash is probably not a big deal. And to the degree the hotel has a restaurant or bar they probably come out ahead. Your hotel may take a different approach but it's near universal (perhaps outside of resorts) that hotels charge the same for 1 or 2 guests.

Citation needed. In my experience it's entirely the opposite: it's nearly universal that hotels charge more for two guests than one.

You can easily verify this on Booking.com, where the search results show price per room and how it varies based on how many people are in that room and whether they're adults or children.

Price only varies for the breakfast-included option in my experience.

I don't care to do research. I will say when I book on Marriott.com there's never a difference. I don’t use booking.com much though.

Is this a non-U.S. thing perhaps? I’ve never in my life seen a U.S. hotel charge more for double occupancy, outside of special packages that include e.g. meals for each guest.

The other things priced into the "experience" are why I call out cruises separately. With a hotel, I get it, a room is a room. But a solo cruiser is eating half the food, drinking half the drinks, taking up half as many seats at shows...

Maybe that's the problem. Cruises rely on people spending a lot of extra money onboard the ship, or drink packages, nicer dinners, excursions, etc... fewer people doing that, with less social pressure to spend extra, means less money for them and they have to make it up somewhere.

Isn't the cruise capacity still limited by the number of rooms? So saving peanuts on drinks and cheap food probably doesn't make that big of a difference for them.

There are a couple travel agencies in Ushuaia that sell open cabins at steep discount for cruises heading across the Drake Passage. If you've got a little flexibility in your schedule, you can set foot in Antarctica for a lot less than if you bought a ticket anywhere else.

Cruises are selling a set space rather than a service or trip per person. The extra incremental cost is minimal for the second person.

Also the more people on the ship means more chances of selling high margin add ons like drink packages, excursions and so on.

Ease is relative especially considering cost, but that's the kind of thing that having a good travel agent is good for (eg: finding someone with knowledge of where to stay in Chile and who to hire for a charter flight or boat trip). Economies of scale kinda kick in though so a cruise is probably the least expensive.

Some cruise lines, like Norwegian, have specific solo travel fares and cabins and even social events just for solo travelers

Ships going to Antarctica often offer single beds in shared cabins.

When I went there, I booked the cheapest bed (maybe $6500 in 2013) in a three-person cabin. It was early season and the ship wasn't full, so the company filled it with backpackers waiting for last-minute discounts in the hostels of Ushuaia. Because I had paid the full price, they upgrade me two classes to a much nicer two-person cabin. And then halfway through the trip, the ship delivered some staff to a museum. The other guy got their cabin, and I got the one we had shared.

Go to Ushuaia, and book a normal ship just like all other folks do. You will have 100x more rewarding experience from all of it, guaranteed. Its not just destination but whole road to it that make such trips worthwhile and you will keep remembering it for rest of your days.

Cruises are for folks, how to say it politely... who gave up on any form of adventure or excitement in their lives. Dont be that person, not yet at least.

I just invited myself along on a "girl's cruise" to Alaska that my wife was doing with her friend (who's actually my second cousin). As the third person in the cabin, my fare only cost $99, plus some fees, compared the several thousand each my wife and cousin paid.

There were quite a few solo travelers we met on the cruise, though - I think they mostly had solo inside cabins with no view.

It is strange balance, but in cruising there is expectation that money is spend outside the base fare on extra experiences. So getting double money from double occupancy is important. Cost of basic food doesn't scale that much. And these extra revenue opportunities is also why occupancy beyond double is so much cheaper.