Why are the questions limited to 140 characters? How can we expect good answers when we can't give the details of the question? Unreal!?

They aren't. Only the SUBJECT is 140. Look next to the submit button on the question. See that page icon that is titled "Details"? That is where you get the additional space to add detail to the subject of the question.

As is outlined on the help pages, https://help.yahoo.com/kb/answers/question-yahoo-answers-sln8239.html?impressions=true

Ask a question on Yahoo Answers

In Yahoo Answers, you can ask about anything under the sun, including the sun, and get answers from real people. Here's how to start asking!

Sign into Yahoo Answers.
Enter your question in the "Ask a question" box.

Your answer may already exist: there may already be an answer to your question under "Existing Similar Questions."
Under "Details," add anything else you'd like to clarify your question.
-The clearer you are, the better answers you'll get!
Click Add photo/video if you'd like to add one to your question.

Image size: images must be less than 5MB and videos less than 600MB and 5 minutes.
Click Submit.
Click Edit Category to select where your question fits best.
Click Submit.