Why is Citrea doing that?
Yes, there are two groups of people doing this:
(1) Stamps: https://www.ledger.com/academy/glossary/bitcoin-stamps
(2) Citrea: https://citrea.xyz/clementine_whitepaper.pdf
The Citrea paper is quite dense but I am referring to this sentence in particular: "A total of 144 bytes are committed, split into 3 outputs, one OP RETURN with 80 bytes of data and two taproot outputs with their script pubkey as the 32 byte data, making these outputs unspendable."
Discussion
They created a sidechain model which requires some data about the sidechain to be accessible to users. Their model also involves a federation and I think it is perfectly reasonable to have each of the federation members store a copy of that data, but instead Citrea opted to dump it on bitcoin's blockchain to reduce the chance of it disappearing.