"so why does it seem so difficult to implement alternatives? (sadly, at least one answer is mundane old electoral politics....)"
I often think politicians underestimate 'how far' 'the public' have 'moved' on 'environmental things'.
That is of course what people say they want - local schools/shops/hospitals/open spaces etc.
SOME of these must be the same people who want more parking, out-of-town shopping, bigger cars etc.
So in some sense politicians are just dealing with what they 'know' people want even if they are saying different things.
People mostly(?) want what they have got, then more of the same and then something else too.
I don't know whether this is 'human nature', the 'inevitable' consequences of 'consumer capitalism' or even the result of Judeo-Christian (and no doubt other religious/belief systems) which (sometimes at least) seem to take a view that the Earth and its resources are primarily there for the indulgence of the Human Race.
Etc...