I would have done it on testnet and then told people "hey look what I made!" on social media, but the author apparently does not want to be known, and since weird transactions happen all the time on testnet, it might easily have gone unnoticed by others

supertestnet

bitcoin

Analysis of 0xB10C's weird bitcoin transaction

Thanks for the great explanation and deep dive, so much info in such complete and minimalistic transaction! What's the need of signing it over mainnet instead of playing on testnet?