I think I know what chord progression you talk about… it’s everywhere!
Two things probably explain this:
1 - A ton of buyers continue to buy that stuff as if it’s the freshest fruit on earth.
2 - No one can claim the rights over basic chord progressions, so people use them over and over…
But keep in mind that a lot of tracks are used as backgrounds to video productions or under voice overs, so I think that’s why many authors go for very basic musical beds with little variations. But I know of a few composers producing more complex tracks that are still selling well, so there’s a place for them too.
About the quality around here, let’s be realist, many tracks are selling for 19$, of which authors get around 10$, more or less, so only a minority of composers record professional musicians in hi-tech studios; the rest of the crowd make do with vst’s in home studios and the occasional guitar track here and there. This might explain that, at least in part.
That said, my opinion is that the quality of most accepted tracks seems to be generally higher than a few years ago.