Ok, so firstly, there's a huge gap between Frankenstein and Dracula and Jekyll and Hyde. So we're not looking at a precise incident.

What ties these novels together, alongside other books such as The White Woman, The Fall of The House of Usher etc is the Gothic genre. If you'd like to know more about the gothic genre in general, I can help you out to some extent.

Your question is more literary than historical, so I hope the mods will forgive me for my answer bending that way too.

The nineteenth century was a time of social upheaval. Gothic novels are often set in strange, unfamiliar landscapes, and parallels can be drawn between this treatment of the 'other' and the Empire. For instance, have a look at this British Library essay by Suzanne Daly for an introduction to this line of criticism.

The industrial revolution and scientific advancement, and especially clashing with tradition and religion, also helped fuel gothic imaginations. Take Jekyll and Hyde where you have science creating monsters and scientists operating secretly, behind locked doors. Stevenson was writing at a time of body snatchers, don't forget. In fact, he wrote a short story about Body Snatching himself. Frankenstein, too, asks questions about man's power to create life and usurp the natural order of things - at a time when the Industrial Revolution was having a major effect on society.

In all honesty, this is a big question, and it's difficult to do it justice here. But there are definitely societal reasons why the gothic was so popular during the 19th century, which I hope I've begun to explain. If you'd like to read further, there's a lot more literary criticism looking at gothic fiction's cultural context out there.