It may be a question of a number of factors, in my opinion. How many button activations on any given day for a mod? I mean, 5 clicks on and off, a couple hundred clicks a day of usage, that's 5000-6000 clicks a month easily for the average mod. Combine that with the fact that liquid leaks out, dust from pockets/purses mixes in to make nice hunky messes. It doesn't help that the viscosity of
eliquid helps it sneak into the tiniest cracks and crevices. Then tack on heat variations of several hundred degrees, physical stresses (those long attys with only a tiny, hollow 510 thread acting as a lever against the mod's 510 connector), plain old mechanical wear and tear (those attys get swapped out, right?), and high voltages and power going through surface mount electronics and factor in that fantastic Made in China QC and I'm actually surprised they last as long as they do!
But I get your point... Always seems like they should still be better made!
And most of mine are still working fine after more than a year of continuous use. Except for a first gen iStick 20 that I opened and quickly shorted when the small metal button "washer" fell across the battery wires! Small puff of smoke and goodbye iStick! But that was all me (and some bad design choices, in my opinion!)