Why do I need to download LibreOffice to get OpenOffice to work on my MacBook Air?

1. This is a user to user forum. You are not addressing Apple here.
2. As users we are not against anything really.
3. Open Office and Libre Office are 2 separate products and have nothing to do with Apple or each other. Apple does not require either one for anything at all.
4. Where are you seeing you need Libre Office to get Open Office exactly?

The LibreOffice developers bill LibreOffice as "the successor to OpenOffice.org, commonly known as OpenOffice, which had its last major update in 2014."

From the diagram on the LibreOffice site, it appears that after Oracle OpenOffice 3.3b came out around 2011, the development of OpenOffice proceeded down one path, while LibreOffice "forked" the code and proceeded down another. LibreOffice and Apache OpenOffice are thus both successors to Oracle OpenOffice.

https://www.libreoffice.org/discover/libreoffice-vs-openoffice/

One doesn't download LibreOffice to get OpenOffice to work, it is a replacement Office suite that is updated more frequently and with a superset of file support over OpenOffice. The document formats are compatible.

I am an original StarOffice user. I used OpenOffice until LibreOffice became available and have used LibreOffice exclusively since. You can use OpenOffice if you like, but it isn't for me.