Perhaps, but if my current employer would let me take a 25% pay cut to drop down to four-days a week I would bite their hand off. Differential preferences are, ultimately, what create a market.

There is, however, clearly something broken in the labour market though. The progressive income tax system in the UK means that someone working a five day week for ~$160k p.a. would only see a 12.5% reduction in net income if they could drop down to four-days per week.