Why is CSV "better" than Excel in 5 star open data schema?

Question

I am reading about the 5-star schema for Open data. I noticed that the data ranked with three stars are CSV files while data ranked as two stars are like Excel documents. I wonder why is that?

Is excel less quality than CSV?

Is it because for excel we need a specific application to open it while we can process CSV easily using any text editor?

Edit

I have been reading about it and I found the followings: **I am not sure if this is correct or not**:

1. The two-star-data is data that is formatted under a Close Format or Proprietary Format, which is a way of storing the data according to a specific encoding format that is either secret or not allowed to use in an open license.
2. The three-star-data is data that is formatted under an Open format or Non-Proprietary Format, which is a way of storing the data according to a specific encoding format that is allowed to use by anyone.

Is that correct, please?

Answer 1

Quality of the file format doesn’t matter. And it doesn’t matter if a specific application is needed for working with the file format (or if there exists such an application at all).

It only matters if the file format is proprietary or open/free/libre.

With "excel", Tim Berners-Lee probably refered to the Excel Binary File Format, which is one of several formats supported by the software Microsoft Excel (and according to its Wikipedia article, it was the default format up until 2007; newer versions seem to use an open format by default, Office Open XML). This format is proprietary.

The CSV format is open, standardized by RFC 4180.

So:

• You can get 3 stars if you use a "non-proprietary" file format.
• You can’t get more than 2 stars if you use a proprietary file format.