I aint completely sure but the best guess i would be able to make is that people , average people want a printer that can fit anywhere, Even in the living room next to there TV/PC.
Doing that with a Ultimaker 2 for example or a Delta is of course not the first choice of the majority, As its to big.
Very good point. I guess putting a huge printer in your house can be a bit of an eyesore.

But i guess thats why most are targetting smaller printers, especially the printers from China since they want it on mass production of course.
I just think it's crazy how many companies are trying to make it in the 3D printing industry, creating printers that are pretty much identical to what is already out there.