I had a similar problem with my group. They were great roleplayers and they loved D&D, they were just never interested in really being heroes or becoming involved in the story apart from cheerfully accepting MacGuffin quests and railroading as yet another excuse for their characters to tear through my lovingly crafted monsters. While this was fun, I felt the story needed a little more. Most of this advice has been said already, but it worked for me, so I'll echo it.
First, I now require every PC my player's make to not only have a background (which they were always really good about), but a reason why they are heroes and adventures. What is so important to their PC that they're willing to risk their lives on a daily basis instead of working a nine-to-five and drinking in the local bar. What is their PC willing to die for, and what motivates them to endure the hardships and risks that will eventually earn them a place in the annals of history. Basically, why does their PC deserve to be a part of the story? It was easy for some, they just wanted to help the helpless or crush skulls for the fun of it. But it was more difficult for others (simple greed starts to wear out as a motivation somewhere around sixth level), but after and adventure or two they figured it out. I even gave them bonus points (in the form of a free magic weapon) if they came up with reasons that were not at odds with other players or reasons why they would adventure together. One of my players did resist, saying he just wanted his character to be swept up in events, which was really just an excuse to kind of mess with me. However, after three levels of blatantly railroading his character under the guise of sweeping the PC up in events, he decided he wanted to get in on the fun the other players where having and came up with not one, but three reasons why his PC wanted to be a hero.
Second, give them something they value, something cool, unique or special, something they'll want to protect. Then, just make sure whatever it is they value, it has an important part in your story. A series of artifacts which the players would never want to part with or a castle which has strategic, financial, or social value have both worked well for me in past campaigns. Nothing seems to motivate my players quite as well as trying to take away their favorite toy or trying to burn down the castle you let them design themselves.
Third, make them absolutely hate your villains, and I don't mean the PCs, I mean the players. Nothing motivates a player or unites a group quite like a personal vendetta against your BBEG. When your players are throwing things across the room and screaming stuff like "Now it's personal! *various cuss words*" you'll know you've done it right. This may seem hard at first, but really you just have to figure out what each player values or likes about the game or their character and mess with it. Just make sure you do it in a fair manner so they don't feel picked on. I once had a player roll up a cowardly bard that really just wanted to sit in a bar and drink. So I waited until he botched a Diplomacy check with a fair maiden, and then made sure my villain's henchmen were their to mercilessly humiliate him and take the girl home themselves. A few more instances like that and ten levels later, that cowardly bard led a ragtag army of peasants against the villain's castle and burnt it to the ground. Another time I had a selfish rogue that couldn't be bothered to help the party in a fight he was so busy trying to steal everything in sight. I had some vampires chop of his arm, and then shortly afterward gave him a magical animated glove the allowed the missing arm to function as normal so he wasn't at mechanical disadvantage. Even though his character was mechanically the same, that player hated all vampires and made it his personal crusade to kill them all. He was so angry at adventuring for 20 levels without an arm, that years later most of his PCs still hate all vampires.
Last, you really have to know your players. Take a look at their character sheets, what did they focus on, where did they spend most of their time. The best advice I ever read on DMing said that "every choice is a wish." The meaning being that each choice a player makes in character creation reflects a wish, a desire they want to play out on the table. Cater to those wishes, and use them to entice your players. You need to understand them and who they are and what they want. Some will love a mystery, some will love a chance for their character to take the spotlight, and some will just love to roll dice and smash face. Give them a hook that caters to your players personal desires and you won't need gold to entice them anymore. My players love mysteries and smashing face. So I gave them a complicated mystery for them to unravel and plenty of powerful monsters to destroy. Figure out what your group wants, and give them adventures that involve it. Once they start to trust you, and what your adventures entail, they'll follow your hooks without a token carrot. As for the evil path thing, as long as your player's characters have goals they're all willing to risk their fictional lives for, you have a story to craft.
P.S. Has anyone else read the "Every choice is a wish" part about GMing? I can't remember where I read it.
