IMO the problem is that people seem to think "oh this is easy" in THEIR situation, so automatically they assume that EVERY SAH parent has it easy. That's not necessarily so.
I am a SAHM technically, as I am a lone parent to 2 dcs in primary school. One is disabled, the other has SNs. They are hard work. As they go to 2 separate schools, school runs take up 2 hours of every weekday. Then there are the appointments during school hours for consultants, paeds, OT, SALT, GPs for various other health concerns, eye problems, dental problems, school meetings for each school, school activities. Around that I need to get any house stuff done during the school day, as they need constant supervision when they are home. I can't do it in the evening as it will wake them up, plus I need to get sleep as ds1 wakes up repeatedly during the night. I'm also trying to slowly get DIY done on the house, as it needs a lot of work.
Today, I have one home with D&V, after having dropped off the car to get fixed. I have a broken tooth, but cannot go in to get it fixed until next week, as even though the dentist could have fixed it today (they had time on their schedule), I cannot go in due to no car and ill child at home. I will have to put ds1 in his wheelchair to go pick up ds2 from school later if the car is not done in time for school run (and hope he isn't ill during that time!), and then do the same tomorrow morning for school run again.
In the meantime, because ds1 is home ill, I'm not getting any of the things I needed to get done today, because he is home (same goes for tomorrow as he can't go back until he's better obviously). This means 2 days worth of things to be added to Friday's massive list of "to do's" ... which is looking like ds1 will likely still be home, so I'll have to do the shopping online for delivery over weekend, as taking the dcs to the supermarket can be a nightmare as ds1 doesn't cope well.
But.... I have had people say to me "oh, aren't you lucky, getting to relax all day while the dcs are in school."
Yeah, sure. So YOUR situation might be the life of Reilly, but not everyone's is. Just saying.