What’s the downside? If someone is fired giving the company anything for free is throwing money away. I had a boss at a startup let me know I was being let go

What’s the downside? If someone is fired giving the company anything for free is throwing money away. I had a boss at a startup let me know I was being let go with two weeks notice. I immediately asked for $20k or else I would walk out without helping anyone transition. He gave me the $20k (1/5th of my salary!!)