But you say many of them would work to the company with opposite values.
Interpretations of other peoples values is largely skewed by their perception, and rarely takes into account the practical realities of working on privacy and security in tech.
There are many, many, many folks who work in positions that allow them to provide for themselves, their families, and their communities while working for objectionable organizations.
Look at all of the public servants who are keeping the lights on and trying to keep the US government running. I guarantee you there are folks who absolutely abhor how the system is run, and despise the leadership and politicians (regardless of which leader is in power), but they show up every day and do their job, and try to help people.
It's not ideal, but when you get a burger it wasn't made from a spherical cow of uniform density either...
Engineers who really care about privacy do not work for Facebook like engineers who really cares about peace do not work for the army.
Any job you take is going to be a blend and balance across your personal passions, values, talents, desire for impact, financial goals and responsibilities, risk tolerance, and alternative available opportunities.
Is it so surprising that one of the largest employers in the bay has attractive opportunities across a range of reasons?
The reverse is not true.
Mozillians at Facebook is not new or novel. There was a time when it seemed like everyone was leaving Mozilla for Facebook. If someone collected the data, tallying every subsequent company worked at for every employee departed, it would be would be pretty unsurprising if the results showed Facebook as the biggest employer of former Mozillians.