Because OP_RETURN was specifically designed for that, and I (subjectively) feel that up to 80 bytes here and there that are included in the block and pay the full fee is reasonable.
Discussion
No, it wasn't designed for it
What for, then? 🤔 I always thought that OP_RETURN was for arbitrary bytes.
Apparently it was to burn bitcoins but you’ll have to be crazy to do that. https://en.bitcoin.it/wiki/OP_RETURN
They exist, though! https://twitter.com/YoshishiSatoshi/status/1668345218821939200
OMG Thank you for your donation guys 🫡😂
Smart contracts. It indicates the transaction spending is invalid.