One of the primary points of having something in "excel format" is that it contains meta-data about how to format things. For example, it stores the font, color size, orientation, etc. of what is in the cells.
There is no real way to do this in a .csv file.
If you need all the formatting, why convert it away from what has what you need?
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors