I think the tele zooms are so common on ebay right now because no one wants them.
There were many craptastic marketers. Promaster, Albinar, Quantaray, to name a few. Sigma, Tokina, Tamron, and Vivitar also put out some craptastics, but some very good glass as well.
These lenses were not made to last, and many are not working or are not up to spec.

But right now, no one wants to lug a shit pipe around on their neck and the serious photographers pay for the better glass. And even pocket sized cameras have 5x zooms these days. There is just no place for these low-grade tele zooms anymore.