How come Dracula doesn’t attack anyone but Lucy?

I think he can sustain himself on less blood than needing to drain a half a human's worth every night.

It's also possible that he availed himself of a few other people whom we do not see. He finds some lonely soul at midnight and offs them to keep himself in fighting trim long enough to focus on turning Lucy.

Then again, there's also attracting too much attention. Too many missing persons or bloodless corpses show up and people start sniffing around. Even if they don't go, "Vampire!" they might go, "Foreigner!" given the era. Who should we blame for this spike in death and disease? How about the new weirdo from Transylvania? So he might be playing things low-key so he won't get caught as easily or be discovered by some vampire hunter. That happens anyway, but perhaps he was being cautious.

Lucy was the only chick in England who whipped her tits out for him

I'm pretty sure he sucked the entire crew of the Demeter dry to the last drop. With the ladies, though, he seems interested in a little bit more than just their blood.

IMHO she was not willing, but easily influenced. When he put out a psychic call for a victim, she was the one who got out of bed and sleep-walked into his lair.

Or maybe walked voluntarily into his lair, because she'd walk into the lair of anything that resembled a human male.

Actually, following Lucy, another aspect related to her is when he chose to take her instead of Mina when Mina chose Jonathan over him causing Dracula's heartbreak. On his way to permanently transform Lucy into a vampire like himself, Dracula does kill a passer-by before managing to get by Quincy and Arthur and smashing his way into Lucy's house to condemn her to the life of an undead soul with a never-ending appetite for blood although Lucy is eventually freed from her vampiric state by Van Helsing and her comrades before they join forces with Mina and Jonathan to avenge Lucy by killing Dracula