Multi-Signature – 1/1 Why would someone use multi-signature?

Today I discovered a transaction that uses 1/1 multi-signature P2WSH input.
675b106c71f110ebca9e6435f49508a07b45d40d38e237d02b89e5506f3b136b

For example, the first input has the following script in the watch:

OP_PUSHNUM_1
OP_PUSHBYTES_33 031f1c516fc9362202883b24fd92e6548776a8f1701baca38b63bbe635da8a82f7
OP_PUSHNUM_1
OP_CHECKMULTISIG

I then wrote a script to find more of these transactions and found that in the last 1000 blocks there were 3883 transactions consuming 1/1 multi-signature input. This costs over 30 BTC: 4d8a475e7a0433ef84baec9ec941342cb31d4194b42dedccdc4503e4acad02f8

Why use this instead of P2WPKH which is cheaper and has greater anonymity enabled?