I think sub £1000 bikes are what's enlarged the market in recent years.
The trend is the opposite Trex, and that's been true for years. As far back as 2002 the sales were predominantly of rock bottom "shopper" SLA e-bikes in the £300 to £400 bracket and the only higher price bike to make consistent but small sales was the £850 Giant Lafree Twist. In the UK the first popular e-bike to top £1000 (just) was the eZee Torq in 2006, but still only selling a little over 600 in that year out of the total market.
By the start of 2008 we had the much larger selling Kalkhoffs with all models at substantially over £1000 and since then numerous others have appeared in the higher price brackets. Over this six year period inflation was low, not in any way accounting for the differences, and inflation has remained very low since.
Conversely many of the lower price brands have been failing, once dominant Powabyke went bankrupt on their low cost models and have returned with higher price Xbikes and Powacycle have also found it necessary to move upmarket. Online cut-price model Mistral folded into AlienOcean. Halfords have tried breaking into the e-bike market with low price models but have conspicuously failed. Numerous other low price brands have disappeared too, more than I can remember, but not one higher price supplier has dropped out. A very few suppliers manage the odd model or two at less than four figures, but they don't dominate the market.
As KTM said above, the low cost rubbish e-bikes that were around did huge damage to the potential market for low cost e-bikes. As a result the area of current sales has long been a rather more selective market that accepts higher prices. In essence we only have a specialised e-bike market in the UK now, the low price possibility not being utilised to any extent.
I doubt cycle dealers supplying low price options like kit fitting will ever happen. It's important to note that the huge sales of e-bikes in their main European markets has been achieved with higher price models and not in any way with budget ones. This highlights the real basis of the UK problem, we are not a cycling country, and until we become one, e-bikes will never be a big success.