I honestly think that the majority of SAHMs with high earning partners are kidding themselves if they think that their partner's earning power is linked to them being at home with the kids. There are plenty of high earners in all sectors who have got to where they are without having a SAHP. It might make life a bit simpler for the working partner, but it certainly isn't a prerequisite for success.
Where both halves of a couple are high earners, it's easy enough to buy in the help of nannies, cleaners etc. If the mother has less earning potential, it may make better financial sense for her to SAH because a nanny/cleaner etc would cost more, but that's about outgoings - it doesn't directly affect the other partner's earning power.
I think there are a few exceptions where SAHPs genuinely enable their partners to earn high salaries. One would be the trailing spouse, who follows his/her partner on overseas assignments - arguably, the partner couldn't take the assignments without the SAHP following (or at least, not without splitting up the family), so if there is career progression as a result of the overseas experience, then yes, I think the SAHP could take some credit for that. Likewise, in families where there are disabilities and one parent is needed as a carer - it isn't always possible to outsource that, and so the SAHP does enable the WOHP to earn.
To be clear, I don't think there is anything wrong with choosing to SAH, and there may be significant benefits for the WOHP such as reduced stress, less domestic work, more leisure time etc. However, I think there are only a few scenarios where the SAHP actually enables their partner to earn a high salary. More often, what is really meant is that the cost of outsourcing the SAHP's contributions to the family are too high to make working a desirable option.