And the reason is that he took the $100m in salary so he can pay as high tax as possible:
"In early 2021, Haraldur sold Ueno to Twitter. In an agreement between him and Twitter, most of the purchase price was paid as salary to maximize the tax he would pay for the sale in Iceland. He chose to pay for tax out of respect to Iceland for the disability benefits he received. Per the agreement, he paid the second highest tax of an individual in Iceland in 2021."
And Haraldur knew that if Elon refused to pay him then Icelandic laws would mean they could freeze operations and seize assets of Twitter there. It's a shame Elon isn't able to utilise such intelligent and talented people!
Realistically, how much would this hurt Twitter? Looking at Elon now, he might just go with it.