Because Bitcoin uses a peer-to-peer network for transactions, each location that is working on Bitcoin transactions needs past data to perform operations. Sometimes lots of data.
Rather than constantly transmit large amounts of data between large amounts of locations (the peer-to-peer network) the Blockstream company has streamlined the receipt of Bitcoin data by transmitting it through satellites in orbit around Earth. This allows anyone, anywhere to get access to the data. It also removes the need for a fast Internet connection or any Internet connection at all.
Blockstream also provides anyone the ability to send messages through the satellite for a fee.
The original message announcing Satoshi's Treasure hunt was broadcast through the Blockstream Satellites on April 13th, 2019. No other messages related to the treasure hunt have been sent through the satellites that anyone is aware of.