The mess is in the "V". RFC4180 leaves value interpretation to the application. It doesn't tell you, for example, when a string like 12345 should be interpreted as a number. So we end up sending numbers and dates and other meaningful values into the ether, hoping that the end application understands what you meant to convey.

XLSX has a cell type for IEEE754 doubles, so there is no such ambiguity. It also has a special date type!