My understanding of "lack of engagement" is that
1) the title and summary are not enticing enough to get readers in the first place
2) or the reader's interest is not engaged enough to finish reading the hub
If this is correct, then the first thing you should look at is your title. Make sure it is short, searchable and to the point. Then, take a look at your summary. Since you have limited characters, you need to write one sentence that will hook readers and make them want to open your article to read more.
Within the hub, you might need to break up text blocks with pictures or bold titles, make short lists rather than descriptions in paragraph form, and add some white space to rest the eye. Adding a poll or video will also engage readers. The longer you can keep them on your page, the better!
Although your question is specifically for low engagement, it's also true that poor quality, spelling and grammatical mistakes and poor content are sure to turn off readers and having them clicking away from your article. When revising a hub for engagement, it's wise to double proof everything one more time!
One more thing that hasn't been mentioned. I think that there are some well-written, engaging articles that are seasonal or on current events that just don't engage readers all the time. An Easter hub in September or a Halloween hub in July might not draw readers year around, but they may become popular again when the season rolls around.