I want(ed) to post an answer to this recent question.
The question was closed as "opinion-based", but the "opinion-based" close reason begins Many good questions generate some degree of opinion, so whether to close or not is a matter of degree. I'm not convinced that opinions would have been so varied or divergent to rate closing the question.
There is of course no difference between the terms except for the writers' expectations for their audiences, and maybe what they think editors will publish.
But there is an important point to be made because of the term "space opera"'s origin as a dismissive pejorative (coined by a fan) of poorly-written, formulaic space adventures as well as SF's long languishment in the literary ghetto.
"Space opera" has come to mean a specific subgenre in the last couple of decades but it used to mean crap that should be disregarded, and there are still people who remember those days. Some people are just gun-shy with these terms. Just look at Margaret Atwood's own struggle to come to terms with her work being classed as "science fiction".
Update: Well I wanted to post answer like this, but it's moot now because the OP deleted it.