Why did he receive such a harsh sentence?

It's a good question but probably because of the amounts involved, Madoff stole billions upon billions and it ruined over 4000 people. Plus, it was timing, the market crashed and everyone was blaming people like Madoff for it. He was the scapegoat and the judge wanted to make an example out of him.

Was it a fair sentence? Probably not, I've seen murderers get less time but it was really bad timing for someone to pull off a crime like this.

I think its the scope.
Like, Wolf guy stole from individual investors, Bernie stole from people who ran investment firms, where people had their retirement accounts, 401ks...he tapped directly into where tens of thousands of people had stashed their life's savings, their nest egg.
The stock market itself is volatile...the investment firms are generally much more careful, take much more limited risks on what they invest in. Its why its generally a good idea to invest in them. By bilking these firms, Madhoff ruined the lives of thousands of people. Upwards of 35,000 people saw their entire life's work vanish virtually overnight. It was pretty brutal and it sent a signal that this kind of scheming wouldn't be tolerated.
That being said, I forget Wolfie's name, but yeah that guy should have gotten a much harsher sentence either way.