FioFio, you have it exactly right. If some people enjoy being at home, that's great, and like you say, there's a huge amount of time in the year when the children aren't in school.
Until I started working a grand total of two mornings a week recently, I had 6 years at home with ALL my children at school. It was (and still is, the remaining days!) fantastic. I could choose what I did and when I did it, including voluntary work at two places, helping out at school, hobbies, not-doing-very-much-at-all time and yes a bit of housework. I could do all this, and more, without worrying one jot about coping with school holidays, TD days, sick days, making it to school events or whatever.
If I think of the last few weeks, I've had to take 2 children to a different town at two different times for orthodontist appointments; take one child out of school to a music exam and then back to school; take one child to a lunchtime concert in the next city; and I've had two children off school on different days. I know working parents have to manage such things, but believe me it's a whole lot easier if you're not fitting it around work, having to eat into your precious annual leave, or trying to justify it to an employer.
And how does the OP know exactly what stay at home people are doing? For the first 6 years of having children, I worked from home, but to all intents and purposes I was 'at home' because I did my work at evenings at weekends. Teachers and even some friends were always surprised to know I 'worked' because I was always at school for pick-ups etc and free to help out whenever they needed me to, often at very short notice.
I have several friends who work evenings or nights - they might look like lay-about mums to the OP but they are as hard-working as other parents, they just work at different times to the majority.