Put me in a large group of people I have little in common with or with whom I have no interest in -- but am forced to socialize with -- and I'm used up in minutes. But with people I can somewhat identify with, and in a situation which offers something for me, and I can go for hours and leave with equal or higher energy than I started.
There's also the matter of the depth of communication. In larger groups, it's difficult to reach any depth since many people may be involved in the discussion (and many people may behave differently or maintain more defensive walls); but 1:1 or in very small groups it's easier to develop trust quickly and have some very meaningful conversations.
I find many larger group interactions incredibly shallow and boring... just an endless stream of small talk with some attention-seeking, posturing, or peacocking here and there.