Cause it's dirt cheap for what it is, and if you go in informed and willing to do a little work the fixes aren't that difficult or time consuming. Just cut and wrap the primary sponge with pillow stuffing to make it circumference type polishing filter, buy and install replacement o-rings, get some rubber washers and large fender washers to distribute pressure across the lid properly from the 6 hold down nuts, and you're done. Took me less than an hour on my first filter, and about 20 minutes on the second. 90% of that time was cutting the sponge with less than ideal tools. All in all the repairs / modifications cost less than $10 total. After you do this you get a filter that'll handle a 120+ gallon tank easily for under $80 and is flat out silent.
A similarly rated but all in all less capable (media costs much more, surface area and flow is not as great) Eheim or Fluval would likely cost you $150, or more. That's $70+ I get to keep in my pocket... or spend on another filter, for another tank. It's a baby FX5.
That's why.
Am I hesitant to recommend them? Yes. People are lazy.
Are they bad filters? No. I own two, and plan to get a third.
