Simplicity reasons. Let’s look at this scenario. I have to account for my day to day spending (checking account). I will have gifts for those I care about. My other solution would be to set up an account exclusively for that gift account. I also have taxes, so I will need an account for that. This could be more than a half of dozen bank accounts that I will have to manage daily.
By me depositing all of that money into a single Swiss bank account, it would make managing easier. To account for things like my gift accounts, I will make note of that in the spreadsheet. Everyone that I will give a gift to, they will get their own sheet in the spreadsheet. As I spend down money on their behalf, the spreadsheet will get that noted in the spreadsheet with a date, amount, and what’s left. If someone I care about has a mortgage, then I will provide the money to them without setting up a sheet for them since the mortgage might take out the entire gift. If not, they will have a check written for the rest of the month. However, most other people will simply get a spreadsheet page, and notagtions of when things were purchased.