I’m sure the ad-driven subsidy on TVs plays a huge part. TV prices have declined as “dumb” TVs have been phased out of the market. A more niche tool like a large e-ink display might not make as much sense from to price this way since ad systems need large networks of users to be relevant.
As a check against this, I looked for 42" computer monitors, which don't display ads. There are $600 4k 42" monitors in stock at CDW, for example. The same size 4k SmartTVs are about $300. So, yes... there appears to be about a 50% discount for TVs vs Computer Displays, part of which could be a subsidy, most of which I suspect is volume driving down the cost of production.
Double check the refresh rate, input latency, and color gamut for your comparisons. Computer monitor user concerns are quite different than tv screen users.
TVs also spy on you. That data offsets some of the cost. They also often have lots of other compromises, from chroma subsampling to overscanning, that make them unsuitable as computer monitors.
people underestimate how long e-ink stagnated: it seems hard to imagine an alternate timeline where e-ink had taken the place of current LED outdoor billboards for example... until you realize we were decades away from LEDs being cheap and robust enough for outdoor signage when eInk was already fundamentally similar enough the tech we have now
The company that owned the e-ink patents couldn't scale properly until they were acquired around 2010: in an alternate timeline where development open enough in the early 2000s, we might have ended up with eInk display modules large enough to be assembled into incrementally larger and more profit driving devices
Even now you see that with eInk store tags for example: imagine if the profit they're driving now had arrived 20 years ago and gotten re-invested
