I think the 30th anniversary $1000 Magic offering was a real shot in the foot. I've also heard bad things about some other 30th anniversary MtG offering, but I haven't been a MtG guy in a loooong time, so I dunno.
I also think the treatment Spelljammer got, which I would generously describe as lacking and less generously describe as pretty anemic, was another big shot in the foot. On top of that, recent adventures have been pretty... thin- Radiant Citadel has a lot of "one and done" adventures that read to me like they don't really have a lot of challenge in them or meat on their bones- and the announcement of a quasi-new edition, along with playtest material that, so far at least, seems to poke the promise of backwards compatibility right in the eye while repeating a lot of the "let's get off the edition treadmill" talk that surrounded 5e while looking an awful lot like a new edition, seems like the kind of thing that would depress sales. But I don't know jack about marketing or sales, so hey.