The real story is that Tyll has said in the past that, paraphrasing, all electrostatic headphones suck. Getting over that hurdle is the first step.
Then, there are some new designs being vetted by the DIY community, so limiting the development exposure is the second hurdle.
As for profitability, the final hurdle, small production runs, with possible warranty issues are just a non-starter from a business perspective, witnessed by HR implementations of the Wheatfield designs - while very dependable units, and still sought after, simply do not have the volume to justify the overhead and marketing.
So, if you want an electrostat amp, build it yourself. There are options.