This is one problem many educators face today---making college students speak during class discussions. If a teacher is lucky he or she might be able to elicit the participation of one or two students in a class of say, 40 or 45. Whyyyyyy???

That is the big question.
Having dealt with different kinds of students for the past 25 years of teaching, I have heard students give almost the same reasons for this reluctance:
1) They are not used to it. They were never trained since elementary to high school to speak in front. The only time they spoke in front of their classmates was when they were asked by the teacher to recite the Panatang Makabayan from memory.
2) They are afraid to be ridiculed or laughed at when they make mistakes. This indicates low self-confidence resulting from poor or inadequate exposure.
3) Feeling of incompetence in speaking English which again is closely related to number 1 & 2.
When students are given more drills or practice in correct conversational English, this will give them the opportunity to use the language as often as possible and improve their fluency, thereby reducing their fear of making mistakes and developing them into better speakers of English.
However, this type of activity would need a lot of feedbacking from the teacher who should be actively listening and noting down errors in the students' use of the language. The teacher should not only sit there and listen to the students commit blunders and not do anything about it. The school did not pay her to just sit down, do nothing but wait for the bell. Her role is to improve students' performance. Feedback should be given at the end of every period, giving emphasis to the most common mistakes students make.
With such a class, the teacher starts with a motivation, reminding students what good speaking means, how important are audience contact and appropriate gestures, the significance of delivering the speech with a punch, the use of humor, poise, etc.
After a very good motivational opening, students begin their activity while the teacher should be actively noting down errors in language and delivery. Ten minutes before the time, the teacher goes up front to give the necessary feedback for the improvement of the students.