Because what’s accurate here depends on the context, and the Python example doesn’t hide that from the programmer.
The same dilemma goes for month calculations: does “3 months ago” mean 90 days ago, 91.3 days ago, this many days into the target month, or this many days from the target month’s end (e.g. to account for 28, 29, 30, and 31-day months)?
Because what’s accurate here depends on the context, and the Python example doesn’t hide that from the programmer.
The same dilemma goes for month calculations: does “3 months ago” mean 90 days ago, 91.3 days ago, this many days into the target month, or this many days from the target month’s end (e.g. to account for 28, 29, 30, and 31-day months)?