Multiple statements can be true at once:

An ordinary employee who is just doing their job and hoping to continue doing their job can be laid off for any number of reasons that are outside of their control. The most common of these is company financial performance, which is both completely invisible and completely uncontrollable for an ordinary employee. Behind the scenes, the decision-makers in these layoffs have very scrupulously designed them to ensure that the people deciding who is laid off have no knowledge of an employee's membership of anything that might be construed as a protected class. This is why they often look so illogical.

A manager who has a problem employee can have a terribly difficult time getting rid of that employee in a way that is legal. My boss had one such problem employee, who did literally zero work after being hired. When my manager had an experienced engineer pair program with him, he literally had to be told what to type, keystroke by keystroke, to get him to produce anything. When my boss called him on this, he produced a doctor's note saying he was depressed and went on disability. Short-term disability can last up to a year, and you cannot fire someone on disability without a paper trail that says "You fired someone on disability, you knew they were on disability, and that is a protected class." Now your lawyers have to argue in court that the fact they were on disability had no bearing on why they were fired.

A person who takes the law as a tool with which to screw others over will do a better job screwing people over than the employee who is just trying to do their job and incidentally wants to keep it, or the manager who is just trying to provide a supportive environment for their reports to do their best work. Because that's what they're paying attention to. If you've got a lawyer combing over case law and statutes to understand the fine points of what you can and cannot be fired for, you can act in ways that ensure that you will win a big payout if you are ever fired. These ways probably bear no resemblance to what our notions of a "good employee" or even a "decent human being" are. But they are effective at collecting a paycheck, potentially from multiple employers at once, and being able to collect a bigger paycheck if your employer tries to get rid of you.