I wonder if Mazda's thinking is that now that estates don't look like converted vans, there isn't much that a hatchback could do that an estate can't.

Presumably in some of their markets, unlike the UK, buyers prefer saloons to hatchbacks. I think the Honda Accord is similarly saloon or estate only. The problem for all non-premium brands in this sector is that you can get a base-model 3-series or A4 for similar money, and the families that you rightly say are the main market often buy secondhand - unless Mum or Dad gets a company car, and then it tends to be Ford/Vauxhall, or BMW/Audi/German taxi depending on how senior they are.