Firstly, there are lots of reasons that people are SAHPs other than to do the housework - because they think it's a better option for the children, because of the cost of childcare, because one partner can't compromise their career (e.g. by taking time off to cover sickness).
Secondly, when my DC are all at school (they aren't all yet), I'll probably be performing childcare from about 6.15 in the morning until 8.30 at night, with around 5 and a half hours in the day in between school runs. Of that, child related household tasks (cooking, shopping, ironing, washing, sorting out admin, tidying, birthdays etc) and things like watching plays/matches/going to school meetings etc will probably use up about 2 hours a day. And I'll do another half an hour when they've gone to be. So I'll be working on child related stuff for about 14/15 hours a day with about 3 hours off. Of course in the holidays (20 weeks a year) I won't have those 3 hours. Nor when the children are off sick. And this is assuming my youngest starts sleeping at night.
So best case scenario, I'll be working an 11 hour day 30 weeks a year. And a 15 hour day for 22 weeks.
If I didn't have children and I was working those hours, say as a childminder, would my partner be reasonable to expect me to do every single bit of housework too?