Because it's all marketing bullshit. In fact that's a good indication that it's marketing bullshit - the fiction that the tip of the self-driving car spear will be consumer vehicles.
Admittedly pre-orders are essentially marketing, but marketing of an actual product with intent to deliver, I'm not convinced it's "marketing bullshit".
I guess it is a mix of both. The SV elite pretending they can do another trick and keeping themselves busy and entertained and Google/ABC pretending they are a growth company (beyond search ads). Why should they bother with worldly billion dollar markets such as office communication equipment (which Microsoft is successfully attacking as we learned earlier today).