I'm a SAHM and my youngest (very high energy) daughter is going to preschool 2 days a week. I have a six year old and those 2 days are used to catch her up as we can't get much done when youngest is home, even though I don't 'work'. I still find it difficult to get stuff done, even though as a SAHM alot of people would say I have plenty of time.
My husband is working from home but we don't see him 8am-6pm as hes in constant back to back meetings in the loft, eldest is home from school, the infection rate amongst young children is low so I don't feel bad sending her in, it's her space she's taking up
If I didn't, and we ended up being home for the rest of the academic year, she would start school in September having had only 2 months at preschool (last year).
I think if you haven't an idea about someone's very specific situation it's best not to make assumptions. I've seen so much on Tattle slagging off SAHM sending their kids into nursery/preschool and it actually really gets to me. You do what's right for your family if it's safe to do so. I'm sure the nursery would have refused to take her if it was a big problem.