Because they are afraid that others will judge their language skills rather than the message they try to convey. Here in the Netherlands everyone is supposed to speak Dutch and English and last week someone posted a video on a popular blog. It featured some Dutch salesman with really poor English skills and all the (Dutch) commenters on that blog were laughing at him. I guess some people can't handle the pressure so they just refrain from speaking foreign languages as much as possible.

the people r not confident to speak good enough.they think that others will make fun of them.

because they are afraid of being laughed by other people.they feel inconfident in their E skill.