I think it's the kind of attitude where it's deemed you are not working but could be, and as a result, you are struggling financially to provide adequately for your household.
I think a lot of false offense is deliberately taken by sahms, and I am one, before you think I'm taking the biscuit. I get to be massively lazy, I'm just honest enough to admit it.
I put DS1 straight into nursery at 3 months. Worked minimally from home. Took my time cooking lovely dinners and keeping the house nice. Did all the household admin. But....I did all those things before whilst holding down a full time job. So pretending I was a full time mummy (I bloody hate that phrase, put it on your CV and see how far it gets you lol) because I was so busy, and therefore incapable of working, was rubbish. It was absolutely the easy option. And if Ex DP hadn't been on a big salary, and we were having to go without so I could sit at home all day, then it would have been not only the easy option, but the unfairly lazy option too.
I'm currently pregnant with twins, and gave up my job entirely at about 11 weeks because I was dying with sickness and I'm a professional dancer, so the two were impossible, and now, fat with a huge bump, physically impossible. That's my career done...as a dancer.
However, I also hold two degrees, and once born, could put the twins into nursery, and go straight into a £70k+ role immediately. I'm not going to, I'm staying at home. Because DH is on a very big wage, so my extra income wouldn't make a difference to our family.
I can honestly say though, sitting at home with the children is, in my opinion, the absolute easy option. I know I'm being lazy. It's a luxury being able to wander around the shops. Make the house look lovely. Cook home meals from scratch. All at my leisure. It really grates on me when sahms pretend that because they've got a child in tow, it's a full time job. It's really not.
It's not to say there is no value of being a sahm. Of course there is. There are pros and cons from both camps. But I think some sahms act professionally offended at the idea that they could get a job, purporting that they are "full time mummys" because if they were honest, they could work quite easily, they just don't want too, so best to act indignant at the very thought that it's possible.