I can think of two reasons why people don't feel the need to check and inflate their tyres. Firstly, radials tend not to be so obvious when deflated unless they are severely down in pressure. A tyre with 20psi doesn't look all that different to one inflated to 30psi, and a large proportion of the population wouldn't think to drive with tyres inflated over 30psi. So, if it "looks" alright, it must be ok.
The second thing is the fitment rate of power steering. In years gone by, with manual steering, you knew your front tyres were down - the steering load increased enormously and the tyres squealed when cornering. Power steering reduces the steering effort so much that soft tyres are no longer obvious. Tyre squeal is probably just considered to be "normal" anyway, by the dills at least.
