Why Haven't More Scientists and Engineers Spoken Out About the Controlled Demolition of the World Trade Center?
1) Most engineers are politically conservative, are probably Bush supporters, and simply cannot bring themselves to question 9/11 and the "war on terror".
2) There is still a large degree of taboo associated with 9/11 for anyone to openly question the official 9/11 story.
3) Many scientists fear for their careers if they speak out. Scientists spend half their lives on their education and building their reputations-- they fear speaking out about a hot-button political issue that might inhibit their ability to get grant funding or diminish their professional reputation. I know a mechanical engineering professor who is convinced that the WTC towers were brought down by some form of controlled demolition, yet this person is very afraid of speaking out because of the negative effect it would have on his career.
4) Many scientists probably have not studied the evidence. In particular they may not have seen the footage of the collapses since 9/11 and may not remember the incredible speed and the explosive nature of of the collapses. Moreover, the collapse of WTC7 late in the day of 9/11 was clearly the result of controlled demolition, yet this aspect of 9/11 is very obscure to most people. If more people were aware of the perfectly controlled collapse of WTC7, it would strongly affect what people think happened to the twin towers.
Update: two other factors related to me by my engineering friend--
5) Conformity-- peer pressure; why buck the trend? (closely related to #3)
6) The mentality of: "It's not my job" to worry about this. "How does questioning the official story help me personally?" "Why should I waste my time on this issue?"
(please see highly related post here)