To answer your title question, instant gratification.
To go a little more in depth, "e-hookahs" and "e-cigarettes" are all the same thing in the end: personal vaporizers. The PV market has exploded, however it started with blu and the like with "cig-a-likes" that everyone quickly began to call "e-cigarettes." The parts started out small but people quickly realized that the components could be enlarged and that there were in fact more ways that they could build one and produce the same effect. Now we've got mechanical mods, box mods, VV/VW devices along with a whole slew of coil types, they just carried the "e-cigarette" name.
They're all doing the same thing, just in different form factors and different titles.