Why does Yahoo Answers have a character limit on questions?

Because it's a basic question/answer forum. If a person can't ask their question in 2500characters off details (1500 mobile) + updates, they probably are asking something either too technical for this forum or that is better suited to discussion, not single answer.

Besides, the longer the question the less chance of respondents taking the time to read it all and reply to each significant point.

because many times some just write yes or no for their answer

You mean Answers ? Yahoo Always has had a Character Limit for Questions

Anyways

Yahoo has Just Added a Character Limit Its to Improve Answer Quality to Stop people from Putting Useless Answers like 1 Word or Letter ETC

to prevent people from writing really long and rambling posts

It is to prevent people from writing long and rambling posts.

Because some idiots will drone on and on about irrelevant issues that have nothing to do with the question being asked. The more wordy a question is the less likely the person is to be posting an rational question in the first place.

Maybe they want more extensive answers.

If there was no limit, bad users would try to bust the servers by posting the encyclopedia as part of the question. The other reason for the 140 (title) and 1500/2500 (details) limits is if you post more than that, other users are not going to read it.

Because it wants high class users

Like all things yahoo, it sounds great on paper but it sucks on the execution.

The character limit was supposed to stop point gamers who only puts 1 or 2 letters for an answer. Well joke is on yahoo because they still give short answers but put a lot of dots at the end. Like it takes that much effort to type 13 dots.