Consistent with your experience, my experience is that one of the major factors in clogging is the ink load -- how much of the ink is particles v. fluid. The MK is the highest. It typically clogs the most. This is probably true within any "family" of inks.
The quality of the printer is also a major factor. My 1400s and current 1430 can go a very long time with no clogs anywhere. It might relate to how well sealed the head is when it's parked. Unlike my 1400 family printers, my 7800 will sometimes show a clogged K after a two week sit. It clears easily, however -- until the head totally crashes, which it just did. There does come a time, depending on printer and degree of abuse (including from thick artsy papers and media), that the head, etc. will no longer clean. For me, that's simply a cost of doing business that is spread over enough prints such that it's not a major factor in my per print costs.
Old carts can also be a source of problems -- all rubber parts lose elasticity, including the seals and sometimes internal filters. Leaky seals can cause bubbles; disintegrating internal sponges clog heads. That said, I've had very good luck with modern empty, refillable carts; they last for years.
Pigment dispersant (not the suspension medium or "clear base") appears to slowly oxidize. The pigments then start to clump ("flocculate"). These larger particles start to fall out of suspension and can contribute to clogs. Don't use ink that is too old. Since the large particles settle faster, don't pull pigment from an old bottle just after agitating it; wait a day for settlement and then avoid the very bottom of the bottle.
There are lots of factors and possibilities for problems, but overall and on average, our modern inks and printers deliver very good results.
Good luck with the printing.
Paul