I was looking for a previous version of Magento CE 1.9.1, but there is only Magento CE > 2.0 on the official website. There're 95% Magento websites still on the older version.
Why are the previous versions removed from the official website?
You can find every release starting with
1.1.1 in this unofficial repo:
You can find the 1.x versions (down to the first one 1.0.0) on the official website https://magento.com/tech-resources/download in the Release Archive tab.