A Certain Degree Of Naivete
I'll try to illustrate what I think are the reasons for this.
The scientific/academic community is relatively insulated from the rest of the world; the people who decide to pursue an academic career for the most part share similar objectives and inclinations. Academia is also less taxing, in general, than the industrial sector: researchers need to achieve, yes, but they don't usually have customers breathing down their neck. Or a fastidious, authoritarian micromanager of a boss scolding you every minute.
Moreover, it takes a screwup of monumental proportions to get sacked from academia, but in the private sector the threshold is much lower.
The scientific community has always been cosmopolitan and very mobile, too. For a researcher it's only common to graduate in one country, get a PhD in another and become a lecturer in a third one, all the while being surrounded by people with a similar history.
Academic life is a quite happy one: working most of the time on what you like, setting your own pace for the job (as long as you meet deadlines); meeting nice people from all over the world, travelling a lot (just fill in the expenses claim form), having parties and not caring if you will wake up late the morning after. Sometimes I regret I left it.
When one is immersed in that environment for long enough, he will tend to think that the rest of the world works more or less the same way, it is only a natural reaction.
There probably is an even deeper reason tho. Scientists and engineers tend to a have a specific personality type: they tend to live mainly in their own minds, analyze and overanalyze problems; the external world - and other people especially - are not their strongest suit (of course not all scientists have the same personality). The stereotypical figure of the scientist is the socially awkward genius, and there is a grain of truth to it.
These are, in my opinion, the reasons why bright people can sometimes be very naive.