Today I noticed a transaction that spends a bunch of 1-of-1 multisig P2WSH inputs:
675b106c71f110ebca9e6435f49508a07b45d40d38e237d02b89e5506f3b136b

For example, the first input has this script in the witness:

OP_PUSHNUM_1
OP_PUSHBYTES_33 031f1c516fc9362202883b24fd92e6548776a8f1701baca38b63bbe635da8a82f7
OP_PUSHNUM_1
OP_CHECKMULTISIG

Why would anyone use this instead of P2WPKH which is both cheaper and has a larger anonymity set?