Personally speaking....
Yes....I have some songs that I never fully finished up or developed further.
Although I do have just a couple of current song ideas ('sketches') I've not completed yet all others are abandoned ideas from my very early song writing years in the mid 70's and felt they were too dated to maintain my interest.
So I continued on to new subject matter and always finished them up to my satisfaction regardless of how much time it may have taken.
For me...it's choosing an interesting, non-cliche subject to write about.
That's the key in keeping me interested enough to finish up....the subject I choose and employing good
lyric writing discipline.
I wouldn't think of myself as a song writer if I'd determined most of my writing attempts never surpasses the 'sketch' stage as you state it.
If it's not a complete fleshed out subject or story line/lyrics....it's only a 'sketch' of something I was too lazy to think through and finish up.
I am aware there are many that would disagree with my take on this subject.

I have no interest in achieving 'variety'....I aspire to 'quality'.
Of course, 'quality' is
ultimately determined by the listeners of one's music.

All of us here have our different approaches to song writing and what we personally want to achieve.
To each their own....a good day to all.