I had an article rejected two days ago because it was too short at barely above 5,000 words. I felt it made a cohesive, relevant argument, but the journal disagreed, thinking I should flesh out the paper. I am viewing this as an opportunity to publish an even better article. It won't take me long and there are a few points I could expand on and publish in a different journal, an article of about 7,500 words.
I am realizing now, also, that this was a conference paper. That is the risk if you only go half way in expanding a paper into its article version.