Why does anyone bother to answer a question with "I don't know"?

I'm with you on this one and most everyone who answered before me is right so best i can do is star you for a great question asked good job

Purely to gain points.

Answers that only say 'I don't know' can be reported as they are inviolation of Don't Rules 1 and 12. You can read the Guidelines here: Rule 1 states: Don't "Violate the questions and answer format" and Rule 12 States: Don't "Post content for the purpose of gaining points"

http://answers.yahoo.com/info/community_guidelines...

Answers that just say "Google it" are violations too:

http://suggestions.yahoo.com/detail/?prop=answers&...

The issue of non-answers has also been discussed in the following Yahoo! Answers Suggestion Forum here:

http://suggestions.yahoo.com/detail/?prop=answers&...

I think more users need to remember the following mantra from the Community Guidelines:

"Before you write anything, ask yourself if your contribution increases the strength and virtue of the community"

They feel if they've taken the time to read the question that they should take the time to answer it. It's almost as if they feel that by reading the question it has been directly asked to them and they're obliged to answer it - even if they don't know what the answer is.

To get the 2 points. And it's against Yahoo rules to do that.

Because they get 2 points if they answer regardless if the answer is right or wrong

I spend time on no answer questions, so its usually one of those with an explaination though.