Because the one that du Maurier wrote sucks biomechanical donkey dicks.
I think I am bringing up the rear on this buddy read, so I'm going to be spoilery - although I will use spoiler tags, in case MBD's book ever shows up!
So, to begin with a hyperbolic statement. Daphne du Maurier apparently thinks very little of men, and even less of women. I make this pronouncement with a sample size of two (Jamaica Inn and Rebecca). I am willing to continue research because du Maurier is a hell of a writer, but at this point, this is my thesis and I'm standing by it.
Allow me to explain. With one notable exception, every single male character of any importance in both Rebecca and Jamaica Inn is a worthless bag of dicks. I include Max de Winter in this, since he's a stone cold murderer. Joss is about as appealing as a rabid dog, and isn't just a stone cold murderer, he's a stone cold serial killer/spree killer. Jem is a horse thief and general wastrel. From Rebecca, the only other man of consequence was Rebecca's lover, and he was also a wastrel, although he never killed anyone, which makes him one of the better of the du Maurier men.
And then we have the Vicar, a delicious, steaming pile of second-hand violence, seasoned with hypocrisy and a bit of kidnapping on the side.
If I'd were married to her, I'd be a bit insulted. The one decent male character in either book was the squire in Jamaica Inn, who actually seems to be sort of a stand up guy.
Then we talk about the women. Four women, three doormats. The only one with any backbone ends up being murdered by her husband (yes, Rebecca, I'm talking about you). Ugh.
So, ultimately, there were things about this book that I loved, but none of those things are the characters. I liked the atmosphere. I even liked the plot pretty well. I guessed the twist early on, but I thought it was well done.
And then we come to the end. Worst ending ever. I reject that ending wholesale. In my ending, Mary Yellan sends Jem packing in his tinkers wagon, takes over the lease of Jamaica Inn and turns it into a well respected, comfortable place for travelers to spend a night.