I think part of it is the worst stuff is generally things aimed at people who are new to fishing. The first set of rod's I picked up for myself and my partner was from argos (all my old stuff went missing years ago) a beginners set that was frankly, terrible (
http://tiny.cc/QuZYx if your interested) the line was this horrible thick white stuff, the reel broke within an hour, the split shot was unusable, etc.
But my fiancee didn't know that it was particularly bad, so we used it anyway, then upgraded the bits. The only thing I have left from the kit (bearing in mind is was picked up in march) is the rods, the disgorger and the mini tackle boxes, everything else I binned asap.
The rods are now starting to fall to pieces too, the eyelets are coming off or cracking. But if I left it up to my partner she'd probably replace it with something similar not knowing any better. Shes slowly starting to learn, but if I hadn't been taught by my grandad and uncle I probably wouldn't know that much better, assuming most of the cheap stuff was the same as any other.
Once you get into the £30+ range of gear the quality jump is huge, but most new anglers who don't know someone who can advise them on buying stuff will tend to plump for the cheapest gear possible to try it out, after all spending £15 on something to try it once then binning it if you don't enjoy it isnt a big deal, but £30 on a rod, £30 on a reel, line, shot, hooks, tackle box, floats, usually some spinners as well because they look pretty, bait etc and you can easily spend a ton and throwing that away after one go will hurt most wallets.