This particular screen is slow even by e-ink standards

Because of the weight of the particles that are being moved. They have to shake them, move them a bit, shake them again, move them a bit again. Moving a blob of plastic takes a lot more energy than what LCD's do: who just moves something like 1 electron per 10000 in the layer between the polarization filters.

The way multicolor e-color displays work is by having multiple size/weight particles that are moved by different field strengths, but require being even more careful (because every field, shaking and moving, will move every particle)

Often for eInk screens the problem with speed is the driver (either code or chip), not the paper itself. For example, many drivers don’t support partial refreshes.

I just bought the B/W version of this screen and read the data sheet. Internally, it is four different screens. So I think (haven’t yet received it) each quadrant takes about 2 seconds to refresh (2 seconds is a pretty common refresh time for eInk). A better driver could do all quadrants at once for a ~2 second refresh.

It’s a niche market because the prices are so unreasonably high. Plenty of people want e-ink displays to use with Raspberry Pis, which would then become prototypes for real products, which would then open up the market. But the e-ink people seem intent on keeping the technology restricted for some reason by keeping the prices high.

Eink is selling development kits which are always more expensive. They even explicitly say on their web site that what they are selling is not intended for consumers or hobbyists.