I had the same thought on my mind but I think it's different as you can't easily switch to another brand or store. There is literally no other option for single developers than paying 10x more. It's like if your mobile operator starts charging existing customers 2x and there is no way to transfer your number to the competition.

There's no such thing as a monopoly on ExtJS. If the pricing is a problem, switch to a different library, like pretty much everyone else in the world.

This is easy when you start a project, a multi-year project would be almost a complete rewrite which would cost much more than a few $K. Sencha nows this and is abusing its position.