As an accountant, I hear similar arguments a lot about when a business partnership or limited company is set up between a husband and wife, but where it's (usually) the husband doing the income generating work, and (usually) the wife appearing on the surface to do nothing, but take a wage/dividend/profit share "just for tax reasons".
It's usually completely a wrong assumption. That's because usually the spouse earning the income can only do that because of the "hidden" support of the non earning spouse in terms of support, both in the home and towards the business. The income generating spouse often works long/random hours which means less/no time for household chores or even business admin, so the "opportunity cost" to them is huge if they can earn a few hundred or a few thousand pounds for being able to work a weekend or work away for a few days, which they wouldn't have been able to do if they'd had to do their "fair share" of household chores, business admin, etc. If a small business admin/book-keeping etc takes a day per week, that's a day's less earning if the self employed person had to do it themselves, so based on a 5 day week, that's a loss of income of 20% - if a "non earning" spouse does that, the earner doesn't lose 20% of their income, which is a lot more than the superficial "value" of a day's admin at say minimum wage! Like I say, opportunity cost!
Same with the spouses of senior/managerial employees. Usually you don't get to be a manager/director by just working a 9-5 week, it usually involves long days, evening/weekend meetings, working away, etc., etc., so they can't help with the housework, shopping, childcare, home DIY, even just arranging workmen. It's unfair for the other spouse to have the burden of all that on their own and try to work full time, in fact, it's probably impossible without other paid help (childminders, cleaners, gardeners, etc), so when one spouse can't do their "fair share", then it's only right the other spouse reduces their working hours so that they can do their own share and the other spouses share!
I've no doubt at all that "some" spouses are just spongers who spend their days pampering themselves and other nonsense, but in the majority of situations, I think the non-earning spouse will do a lot more than their "fair share" of household tasks, taking that burden off the full time (or more) spouse, which enables them to work longer hours/work harder, etc., and thus have a higher income.