I've no idea about "Wallet Name" field, but i'm sure it's not part of transaction format, unless the field is about OP_RETURN data.
There are many purposes, but mainly it's used to know address used by scammer/hacker, exchange, casino, individual who have main reusable bitcoin address (mainly for identity verification), etc.
BTW, there are other similar website such as
https://www.walletexplorer.com/bitcoinwhoswho.com seems to have "borrowed" wallet IDs from walletexplorer.com, see e.g.
https://www.walletexplorer.com/address/1FBCBH482Q6MTayQGg8GB4Qf21vKuPHL7ywalletexplorer.com (AFAIK) determines "wallets" by linking addresses via multi-input TXs, the idea being that if two (or more) keys sign the same TX then
likely those keys belong to the same entity.