I was thinking about this, too. In areas where housing supply is constrained, the increasing prevalence of dual incomes means people can bid higher, more competitive offers on housing. And of course they do, because why wouldn't they?

I would even expect this to be true, though on a smaller scale, in areas where housing supply isn't constrained, since, in general, each individual house is unique to some extent; two dual-income families fighting over the same house will have more resources to throw at their bids.