Why would someone use 1-of-1 multisig?

Question

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

I then wrote a script to find more of these transactions, and it turns out in the last 1000 blocks there were 3883 transactions spending 1-of-1 multisig inputs. This one spends over 30 BTC: 4d8a475e7a0433ef84baec9ec941342cb31d4194b42dedccdc4503e4acad02f8

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

Answer 1

You may be looking at transactions of an unknown entity dubbed "Crazy1o1". To my knowledge, it is still unknown who they are or why they are using 1-of-1 transactions, but they've been active for years. Notable mentions:

• LaurentMT first describing and naming Crazy1o1
• LaurentMT analyzing some traffic of Crazy1o1
• Stepan Snigirev asking about 1-of-1 transactions
• Crazy1o1 consolidating 720k+ UTXOs at over 100 s/vB while the mempool was essentially empty
• On-going traffic of 1-of-1 multisig transactions
• Crazy1o1 on OXT.me

Update: LaurentMT suggests that Crazy1o1 is a “Crypto and Forex broker named KOT4X”