His motivation was twofold... First, Morry was risking other people finding out with his bigmouth... Secondly, as we see later in the film, Jimmy was a jerk who wanted to keep more of the money for himself and kill off witnesses to his crime. He became increasingly ruthless...

You answered your own question. Morry kept holding out on money that he owed Jimmy, which was a bad move. Then, later on, Morry wants to get paid for the Latanza (sp?) heist. But at that point, it's more about Morry just running his mouth too much and driving Jimmy crazy. So, in a nutshell, I'd say it was money issues and a big mouth that made Jimmy hate him.

Yeah, and how much money did Morry lend from Jimmy?? Apparently $3000 seems like chump change to these wise guys.

Now did Morry help them with the Latanza heist?? If so he should get his money/share.

But my main wonder is WHYY did Morry borrow money from these psychos to begin with??

Also was Morry a made man?

In the book and real life, jimmy suffered from Insomnia. He would be awake late at night, turn on the tv and see Morris wig commercials playing non stop. It would drive him bonkers according to the book

Hilarious.

In the movie at least, Morrie seemed to get on everybody's nerves. He had a big mouth, broke balls and to be fair even if Morrie only owed Jimmy 30 bucks Jimmy didn't want to be jerked off by anyone especially a weasel like Morrie. But here's the catch. Movie "Morrie" didn't actually exist. The character is based on Martin Krugman, a Lucchese associate who pretty much got on with his own business. He ran his own numbers and betting operation from a room over his hair and wig salon. He would hire Paul Vario's goons from time to time but stayed pretty much independent of Lucchese scams. His involvement in the Lufthansa heist was introducing smugglers on the inside to Jimmy and Henry and really did break balls over the half a million cut he was owed. The details are unclear but ultimately, who the hell knows why, Jimmy figured Krugman was holding back money owed to him from one of Krugman's sports books, there's never even a mention of him borrowing money from anybody. In the end Krugman was becoming a nuisance on so many levels Jimmy had him killed, but not as portrayed in the movie. Tommy was already "missing" at this point, a fact Krugman continually questioned which made him even more of a nuisance. Eventually Burke arranged to meet Krugman at Bonnano Capo, Vincent Asaro's night club and Krugman was allegedly killed there, dismembered and disposed of at Asaro's fencing company adjacent to the club.

@GlompsAndNibbles said:

Ego. Simple.

Jimmy was egotistic just like Tommy. They had been a long way into the business and demanded respect. When you are asked to pay by the mafia then you better make sure to pay on time. But later when you try to be a pain in the neck by pestering people like Jimmy and Tommy then you are heading for a dirt nap.

In both real life and the movie Jimmy and Tommy were never made men so they were never in the mafia.