The original Kr8 cartomizers were/are 3.0 ohms. The newer ones (e.g., Vapor4Life's Premium and WOW, CigEasy's Gold Label Deluxe, and VaporNine's Turbo) are less than that. Exactly what, I'm not sure. NHaler's Mega LOW RESISTANCE Cartomizers are stated as 2.0 ohms.
I don't know what you mean by "why." If you mean, why are/were Kr8 cartos higher resistance than the 510 atomizer, part of it is explained by the higher voltage battery Kr8 cartos are used on. The Kr8 batt is a true 3.7V; the 510 batt is more like 3.2V. [Even the eGO is only around 3.4V.] And to get into the details of the relationship between volts and ohms (i.e., Ohms Law), you may want to read
this article. It explains (simply and easily, I believe) the what of watts and why we vapers care about them.
Also,
all of the first round of atomizers (e.g., 801, 901, or Kr8) were higher ohms than most North Americans or Europeans like. I have suspected that they were geared to the taste of the typical Chinese vaper. It was we westerners (i.e., Cisco) who came up with the LR atty.