Sharing knowledge, as all worthwhile things in life, can be fun as well as practical.
Some people feel that fun and building a good free encyclopedia are distinct; perhaps even at odds with one another. They actively chastise people for having 'irrelevant' fun or engaging in 'silliness' even if those do not both other community members -- for those activities are distracting the editors in question from more useful work.
Others, with long respect for and understanding of the open origins of wiki, as philosophy and collaboration -- and as origins of wikipedia -- have a hard time imagining the point of view described above.
Wikipedians who believe that one should edit often and enthusiastically, without distraction and without socializing, tend to make a preponderance of edits on detailed policy pages, and on specialized deletion pages. They have a significant say in how some aspects of Wikipedia policy develop. They are likely to know by acronym and number all of the CSD rules and the shorthands for recent arbcomm cases. They do not see an equidistributed cross-section of Wikipedians in most of their daily discussions; similarly most Wikipedians do not in their daily editing encounter opinions strongly held in these policy debates.
To clarify the origins of recent attacks on being sociable, I am gathering some of the rationales for banning fun on Wikipedia below.