Well they are getting a 75% discount to bloat the UTXO set thanks to bad incentives, so as has been discussed there is no reason for them to use Op return instead. So far that seems to have been the case: nostr:nevent1qqs97kyqzhumg3spvtjqhz2xpakz6ezgmmgrcc84y7wl49rxa2t43hspzemhxue69uhhyetvv9ujuurj...