50 Shades of Grey is smut with a stamp of approval of a large publisher. They allow it once in a while as a way to monetise human sexuality otherwise repressed and controlled by various powers.
50 shades of hot garbage, unironically, is one of the books that brought smut back into the mainstream. As much as I have no interest in reading the series, have to give credits to the author for making something incredibly popular. We can hate it, but there are millions of people who read and write fanfic on a daily basis, and targeting that audience is respectable.
But I agree, being on bestsellers list nowadays doesn’t even as much as it used to. Everyone’s up there to game the system, whether through extreme SEO-boosting or buying their ways into shortlists and recommendations.
50 shades is laser targeted. To the point that I tried reading it and abandoned it before 25% because the laser targeting is extremely precise and missed me :)
Just because it's not depressing oscar bait or space opera it doesn't mean it doesn't have some merits.
Although i find it hard to believe it was done as a "labour of love".