I'll say this that I didn't say before - I think preschool is a clever marketing scheme designed to fleece well-intentioned parents. It preys on the fears of "my kids won't be good enough" or "my kid won't be smart enough" or "my kid will be at a disadvantage" and I could go on and on all night. I almost forgot to mention how much preschool helps the "gifted" children (what child isn't gifted these days). The majority of preschools are in daycare settings. Around here they are called "Mother's Day Out" programs
I so agree with you here. In my younger days

through college, I worked as a pre-school teacher (in a childcare center that was NAEYC accredited) and it was a wonderful school with wonderful teachers.
Flash forward several years...Last year DH and I thought we might interview a few pre-schools for our twins and were unpleasantly surprised at how little "education" it appeared they would receive. The had lots of sand tables,
lego tables, doll corners, arts and crafts table, etc..., but there was no sign of the educational experience we were looking for. We weren't going to invest that kind money for our kids to "learn through play." They can do that with their friends or at home. So, we didn't feel it was worth it. The only place we found to be in line with our kids personalities and needs was a private school that was upwards of $12,000 per year, per child, which we thought was ludicrous for a 4 year old.
So, I put together a lesson plan for them and have "school" at home (for 1-2hours per day), and they already know everything (and then some) a child is required to know for graduation to 1st grade. I know in my heart that they couldn't get that undivided attention in a pre-school with 20 other children with 1 teacher.
Now, I am not against pre-school (obviously, I used to teach).

I do, however, think it depends on the child and their needs, not what society dictates.