If we ignore the low pay, physically demanding work, bad benefits and and unpredictable work schedule, then yeah I guess these jobs sound great for moms.
Physically demanding? What's the difference between cleaning a hotel room and cleaning your house or bedroom? There's absolutely zero heavy lifting. You change the sheets, vaccuum and wipe down everything.
I would option to say taking care of kids is more physically demanding than cleaning.
If it's just supplementary income it wouldn't really matter about benefits as the spouse would already have benefits.
Zero breaks, for one. And no ability to take sick days/stop doing it if you're injured. Doing work for 1-2 hours a day or a few hours a week is very different from doing it for 20-40 hours a week. (Much like there's a difference between taking on a project or two for a small team that requires some programming and being a full time dev). Oh, and you can't sit. That's like saying anybody who mows their lawn would have no difficulty in a landscaping position.
And the kid thing it strongly depends on the age and type of kid. Kids at the most physically exhausting ages also tend to take naps which gives the parent a respite. You can also trade off with the other parent/other relatives if you're tired. Can't do that with work: Your coworkers aren't going to do your job if you have an off day.
The physically demanding part is in the demand for physical consistency.
C'mon man. At least have a serious argument. You act like a person cleaning a hotel room can't stop to use the bathroom or take a few moments to collect themselves before starting on the next room.
Have you ever stayed at a hotel? The staff moves at a normal rate, there doesn't appear to be a rush, they aren't sweating through their clothes. I've seen staff in their phones, texting, changing their music.
Not in room cleaning - I was a dishwasher - but yes, I know how it works.
If you think 3 minutes in the bathroom is the same as an actual break, it's not. They appear not to be in a rush because they have to set a sustainable pace. That doesn't mean it's not difficult, especially for females. Many things that are easy for males physically are a PITA for us.
Being on your feet all day and bending over to scrub a toilet is physically demanding relative to a project manager sitting in front of their laptop. Yes it's not as physical as working in a moving company, in a steel mill, or as a home health aide who lifts disabled people. "If you've got time to lean you've got time to clean."
There's not always a spouse with a good job. When the employment market is in favor of employers people just have to accept shitty jobs. In tight labor markets these low wage no benefit jobs are hard to fill and current workers at an establishment don't lose much by quitting for greener pastures. Even with a spouse who has benefits through work, many employers don't subsidize family benefits. Their solution is a "spousal surcharge."