I think the death of high-streets is largely a council inflicted problem. Not an ounce of business sense between them.
Instead of thinking, "How can we maximise footfall, so shops do well?", it's "How can we extract as much money from drivers and shops as possible?"
In my home town up-north, the council got rid of the carpark in town and replaced it with a ginormous bus-station. Result: Shops going out of business within months as all the commuter shoppers had no-where to park going or coming from work.
Waterlooville where I live now. There was a carpark next to Waitrose. Council kept jacking the prices up. Waitrose left, high-street on life support. Now they've made the carpark free to try and get people back. Should have done it before Waitrose left.
There's a reason why supermarket carparks are usually always free. They know what they're doing.
There is zero reason why council owned carparks have to charge money at all. Make it free for say 1 or 2 hours, and people will nip in and out and use it. I'm not going to pay 3 quid parking when I can get free delivery online.
Edit:
There's also the problem of range.
I went to next to look for some jeans the other day. Had nothing in store in the size/fit I wanted. Until shops start holding more range of things, they'll struggle to compete with online.