Don't agree Trex. Those remote "home town" sellers have for years done most of the sales. Back when this forum started the biggest selling quality e-bike was eZee, from Loughborough. More recently the Kalkhoff brand has been one of the biggest sellers, also from Loughborough.the location of those internet based sellers is determined by the home town of their founders - the bulk of sales is through traditional distribution, some 500 LBS that do both sport bikes and e-bikes and about 50 e-bike specialized retail outlets. The last few openings are in London, that proves my point.
The first specialist e-bike seller opened in Cambridge, population 124,000, while during their early years there was no specialist e-bike seller in my London borough and the immediately surrounding boroughs with 1.16 million population. Cambridge became a major e-bike supply centre with other companies based there as well, while my London borough with three times the population of Cambridge had a discounter with a couple of the old heavy Powabykes on offer and a very large bike dealer who sold one Giant Twist a year on average and didn't always stock it. Neither could be tried. Even today South London is, in relation to the 4 millions living there, an e-bike desert for supplies.
That first specialist seller in Cambridge, Electric Bike Sales, went on to open branches in Oxford, York, Bristol, and only last of all more recently, London. And of course Cambridge and York have long been the country's major cycling centres, with Oxford and Bristol also being cycle popular areas. As a result of the congestion charge London has also become a cycling heavy area, hence the recent growth in suppliers here that you mention.
Clearly population has not been the driver for supplier location, it's always been where cycle commuting and general purpose cycling is popular. If population had been the driver, the suppliers would have always been here in London instead of only turning up recently. Even today in my Borough of Croydon which is London's largest borough with over 370,000 resident, my best bet to try some e-bikes is to go outside London to the (fortunately close) Surrey town of Coulsdon, population 25,000.