[notacoward]

As others have said, there are other possibilities. Some good, some neutral, perhaps some bad (but in ways unrelated to how Facebook itself is considered bad).

A great many are there to build their skills and/or resumes, which is a lot more than just putting food on the table. There aren't many places where one can learn so much so quickly about certain technologies (like VR/AR) or how to run things at that kind of scale, and most of those (e.g. Google, Amazon) have their own ethical issues. Many other companies, including some HN darlings, were founded by ex-FB employees. Some of them are doing good things, for practically any definition of "good" you might apply.

Others are there because they believe in the good Facebook does as well as the bad. As you said, they're likely exposed to more information about what the company does, which means a lower percentage is of the "jealous columnist at NYT" variety. Facebook helps connect people and businesses in positive ways as well as negative. You might think the ratio is not high enough, but others can quite reasonably disagree and/or think it's worth their time to work on improving that ratio.

There are many other possible reasons as well. "Evil or trapped" is not a useful simplification.