What are the specific reasons for lacking communication skills by our engineering graduates coming from out of colleges?
Most of the Engineering Graduates are lacking communication and presentation skills. They are not in a positon to learn behavioural changes, personality traits and official decorum and decency to find a better place in their career.
There are several different ways this question could be answered, and almost all of them are going to be based primarily on observation and opinion. First of all, your question makes a very large and generalization about "most" engineering students , but rather than argue with the potential fallacy here, I'm going to suggest that engineering students who graduate with a lack of general communication and job readiness skills do so for the very same reasons that any other college graduate (no matter the major course of study) does, and that is this: most college graduates lack life and job experience.
Even the best university programs (again, in any major) which require "field work" or professional "practicums" within major courses do not, and I might argue, cannot fully mimic the real working world. I would personally submit that this is because the students are still in a time of learning, but while in undergrad, the only consequence, or risk, at stake, is a grade, and not the loss of job or higher salary. Add to this that many students are not financially responsible for themselves while in school. Whether living and studying as a result of student loans, scholarships, or family funding, there is certainly a different mindset when a person's work is directly affecting his or her own livelihood.
Finally, I think there are many who would cite technology as having a negative effect on verbal communication. Most college students communicate primarily by texting, especially at the beginning of a relationship. As a result, these 20-somethings are effectively avoiding face-to-face communication practice in new situations. If they cannot even talk to their own peers without the protection of a technological barrier, imagine how a professional interview is going to feel.