I am the sole income earner in our household, but my wife and I have separate checking accounts. It’s not a matter of whether it’s my money or hers, but just a convenient way to isolate spending to reduce lines of communication. Early in my career I wasn’t earning a lot, and having to coordinate spending around a shared account led to more than one overdraft charge. Yes, this could be solved with careful communication and planning but that’s overhead we didn’t need or want to deal with for day to day spending.
Larger purchases we have to coordinate on, but the communication is important there and less so on whether me splurging on a nice lunch with friends is going to impact her paying for school clothes.
Technically both accounts are joint accounts so it’s definitely not about hiding purchases or income. It’s just a logical partition around our daily spending habits.
We have been married for 16 years and together for 23. We don’t ever fight about money.