Speaking in the context of UK society (i.e. dominant religion is Christianity, or debatably now atheism... )
It makes no sense culturally, because why would the week start halfway through the weekend?
It makes no sense religiously, because surely we're taught that God made the world in 6 days, and rested on the final day. Hence, we too rest on the final day. Why would the week start on the day God finished?
Is there something I'm missing?