As for why I think this, it mostly is down to what such bikes can do which cannot be done by other, more common bikes.

Velomobiles are faster, the most energy efficient transport currently technologically possible. They are safer because you are protected by a shell. They are more comfortable because of a recumbent and more relaxed riding position.

Inside city traffic an upright bike is more agile and it requires less space at home. But those are I think the only insurmountable downsides of a velomobile.

But we’re reaching some limits with speed. A class 3 ebike can do 45 kph (28 mph)

You need insurance, regulation make it much harder / more expensive to get a new model to market, you cannot use bicycle lanes and you are not allowed to park on sideways. And they are less comfortable than recumbent bikes. And their payload is limited because of high center of gravity.

The ideal would of course be more lax regulations so you can have e-velomobiles or velocars that can go up to 50kmh.

Essentially, I think the market is really narrow for velomobiles, with no reason to expect it to grow substantially in future.

I think outside of pure micromobility in dense city traffic you are wrong here. Velomobiles do need to evolve to something more practical and away from the enthusiast speed machines (more like the frikkar podbike) and the prices and regulations and infrastructure has to be improved. But to categorically reject them because "45 kmh mopeds exist" is a disservice.