I read the Mail link in post 1878#. It sadly reflects many cities and towns in the UK. There does not seem to be one particular answer and it there is no point in illustrating only one aspect to declining retail outlets. There are, it seems, a few reasons, which, when aggregated, have brought this about.
However, judging from the photos on BHF showing the continual demolition and rebuilding of parts of the city centre it does seem that many are voting with their feet. Post WW2 the population were more resilient - having survived a horrific war - moreover public transport played a great part of their travelling lives. Today that is not so; a large part of the population have their own transport but prohibitive car parking costs and restrictions have encouraged many to seek out of town areas where parking is easier and usually free.
Birmingham should attract lots of punters from the rural areas outside the city but I am of the opinion that the reconstructions - and some of the things highlighted in the newspaper report - may well have diverted trade elsewhere.
Sadly much of the townscapes these days consist of food and drink outlets. If I stand at a crossroads in one small Devon town I can see six places offering coffee and food, some alcohol. The rest of the town is tourist orientated, has the usual 'charity' shops and most banks are closed down.
We may blame many things, but when all said and done we either support the shops or we don't. Is it much of our own doing? Noticeably some areas of our cities are busy; that is the suburbs where the local population is supportive.