Work life balance. One track. The "Run away unless you have no other options" review sums things up with an entertaining story, albeit slightly hyperbolic. Broadly, everything boils down to $
The company only cares about making the company money. Historically, if you were a fresh STEM PhD and liked to talk with people/do things other than super intense focused research, you didn't have very many options for a career, so that created a fantastic pool of fresh PhDs for Exponent to hire from. Who cares if they only stay for 2 years or so, since we can just hire more to replace them? And since Exponent generally charges by the hour, if someone brand new takes twice as long, as long as the client's pockets are deep enough, great, we can bill double. (more money for the company!). If the client's pockets AREN'T deep enough, who cares, we'll just not let the new person (or more likely, the squeezed manager in the middle) bill their time and then the company still makes the same amount of money, and the company just doesn't pay that squeezed manager or new hire as well. The company is doing just fine. Once you realize that making Exponent money is literally the ONLY thing that matters to Exponent, it's very easy to see the rationale of all their choices.
Now, you may ask "well what about all those studies showing that it costs more to hire someone new rather than retain someone?" To that, I redirect you above to the afore-mentioned "new people may do things slower so you can charge double." The value that a good team player who cares about his colleagues, actually teaches them things on the job, and helps set reasonable deadlines (another skill that can get honed while at Exponent) can't easily be counted in dollars and cents (ironically, those traits are "invaluable," or "priceless" which Exponent translates to "not valuable" or "can't charge for that - there's no price!"), so since it isn't easy to translate that to $$ for the company, Exponent doesn't care about it.
There's really so many terrible things about working at Exponent that it really isn't worth typing them all out, and in some sense, doing so would more likely diminish the potential value of this review to potential candidates looking for that first job out of grad school. I'll stick to the "Exponent only cares about making Exponent money" because every single bad thing about the culture can be traced back to that statement.