Unfortunately I couldn't find a better writeup, although I remember it.

The basic problem was that they transferred into his "cold wallet" https://www.nerdwallet.com/article/investing/hot-wallet-vs-c...

He didn't want to have the signal be that he was happy holding SHIBA and was uncomfortable with that much power & control over SHIBA. So he wanted to be able to transfer his SHIBA out to a hot wallet and then burn most of it and donate the rest, given the amount of money involved he took extra steps like buying a new computer to generate the new keys, airgapping it from the internet while it held the cold wallet keys etc