The high street is being decimated by the fact people have stopped shopping there and therefore the nice normal businesses struggle to earn enough through sales to stay open
This is exacerbated by the fact that a lot of local councils charge very high rents for shop fronts. They do this because council revenues are otherwise very restricted (there are tight limits on how much you can raise council tax) and costs are increasing (social care etc)
The only businesses able to pay the higher rates are vape shops and barbers. Since selling vapes isn't that profitable it's reasonable to assume they can afford this because they are making money through dodgy means. Eg drugs under the counter. Barber shops are a good way to launder money because they offer a service not a product. If they were selling chips it would be easy to see they were claiming to have made X amount profit but hadn't bought enough potatoes for that to make sense but barbers only need combs. It used to be tanning salons for the same reason.
There is a suspicion that in some cases councils are happy to turn a blind eye because at least the shops are open and they are taking in revenue. If the shops are facilitating drugs or money laundering then thats a bad thing. However proving this and shutting them down takes time and police attention (this does happen). But while not all barber shops are linked to criminal gangs it's not a myth that some are.