You can get phones with the same SoC for half the price. Yes.
Now try it the other way: Look for how much you can get a current phone-like device with a hardware keyboard. For non-sliders there are a few options, but those won't let you get away much if any cheaper and may even sport slower hardware.
This is the price of niche hardware. I don't doubt we all wouldn't mind a lower price.
But there are many factors in this. Low volume, unknown demand, high development costs, just to name a few. Economy of scale makes it worse. They also need to profit a bit on this to stay afloat.