They can't survive in isolation. They relied on other shops to draw people, i.e. parades of shops that used to be all over towns, the "high" street even in small towns and villages, etc.
People aren't going to go to the out of town supermarket and then stop off at Mrs Miggin's fishmongers on the way home, especially when the council have pedestrianised the road or put down double yellows and other traffic calming meaning you have to park, pay, and then traipse down to the shop!
Peoples' habits have also changed. Now women work, they don't go shopping every day or two and instead do a "one off" every weekend or even get it delivered.
We had a family newsagents back in the 70s, 80s and 90s. It was on a parade of around a dozen shops, including greengrocer, grocer, butcher, fishmonger, chemist, hardware shop, bakery. A bloody great Asda was built at that end of town and trade dropped virtually overnight. Over the subsequent couple of years, the other shops closed one by one leaving us the last shop standing, but trade was dead and ours ended up closing too. Before the Asda, people would come round and go to 2/3/4 different shops, but they went to Asda instead, and the number coming dwindled as the shops closed and there were fewer shops to come for.
So, to answer you question, the shops closed because their customers stopped using them!