I think they did it for marketing reasons but they do have statistics that the Ribbon interface is easier for (new) users. Essentially, the old menus were replaced by the Ribbon tabs. You are very late to this pity party. The change happened in 2006.
I bought, but never used Office 2007 because I thought it a step backward. Word 2010 was much better.

You can still use Word 2003 if you have it.

Otherwise, here is a link where you can download the Word 2003 setup to work in Ribbon versions. Search the page for "Classic UI."
Ribbon Menu Control - Classic UI tab - by Greg Maxey