They just suck.
I was startled out of my mind to find black cartridges for my Canon Multipass F20 at Best Buy for around six bucks a while ago and bought one thinking I had gotten a great deal.
The printer is usually pretty good at telling me when it gets low on ink - or so I thought - but I found out today after reading the manual a bit that the warning goes off after a set number of pages are printed with a cartridge. Which is why when you open the access the door and close it again, it asks you if you changed either of the cartridges because if you did, it resets the counter. This is a great system - UNLESS - your cartridge manufacturer/remanufacturer only fills the tanks half-full. My black has gone completely dry and I haven’t even gotten the first warning let alone the second one. (With every other brand of cartridge I’ve used, it usually starts acting funny after the second warning).
I won’t buy that Dynex crap again.