I think that's because in the Hobbit, Elrons was presented as less complex, only wanting to help Thorin's party on their way armed with the information and supplies they would need to attempt the burglery of Smaug's hoard from the Lonely Mountain.
In LOTR he had a lot more on his mind, like: what would happen if Sauron gained control of the ring, if Frodo tossed it down the tube; what to do with his daughter who was making eyes at Strider, that ranger bum; then in the library, there was those scrolls from the first age, that were deteriorating at a rapid pace and something just had to be done about them in the next couple of decades or they would be forever lost to posterity. So much responsability, so much time, so little help. *teacher
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