Why haven't competitors entered the market with cheaper products?
They did. Windgap[1] took venture capital, took state funding from Massachusetts back in 2012, and didn't ship the product. Cool web site, though. Sanofi tried, but their product misfired at least 26 times and was recalled.[2] Teva tried, and their product was rejected by the FDA because of problems; they're going to try again with a new model in 2017.[3] [1] http://www.windgapmedical.com/ [2] https://www.auvi-q.com/…
It sounds like it's harder than we might think to make this work.
Given that, and the low volumes, it might not be that profitable even at $600 per sale.