To managers who had to let someone go but were forbidden from giving the real reason: What was really happening, and what stopped you from telling them?

I know that when people are let go, they're often told very generic things like 'we're going in a different direction' or 'you're not a good culture fit.' This is usually code for things that can't be said out loud, like 'your attitude is terrible,' 'no one on the team can stand you,' or 'you're not smart enough for this job,' so the company avoids lawsuits.

But at least that gives you an idea, even if it's vague.

What I want to know about is a situation that just happened to a colleague I used to work with. He was let go a few weeks ago, and his manager told him explicitly that they were instructed not to give him any reason at all.

I imagine that sometimes there are improper and illegal motives, but what are the other logical reasons that might make a company do this?