I regularly read two science fiction periodicals, one of these likes to think itself more hard-core than the other, but my post applies equally to both.
It seems to me that, over the last 10 years in particular, there has been a major increase in the number of time-travel stories published in these magazines. Some are very good and I enjoy reading them, nevertheless a time-travel story seems to me an easy way for an author to claim they are writing "science fiction" without having to come up with a truly novel idea.
I wonder whether this is due to authors being less inspired about themes that have traditionally been thought "science-fictional". Perhaps it is because technological advances have accelerated so there is less eager anticipation of the future than before.
Does anyone think that time-travel stories should be given their own category separate from "mainstream" science fiction? BTW I think I have a broad definition of "mainstream", I'm not just including "hard" science fiction which I consider a subgenre. Nor would I exclude something like "new weird" from "mainstream".