Why is Buddha almost treated like a God in most Buddhist traditions?
Simply I can tell you this. When Buddhism was invented in certain countries, it mixed with their culture and believes. So if you want to filter what Buddha really said, you have to refer The Pali canon. Actually in "Mahaparinibbana Sutta (Maha vagga - Digha Nikaya)" before The Blessed one passed away, when gods and humans are worshiping him and paying their last respect, the Blessed One stated that: 


  "This is not the real way (by offering flowers etc) that you can pay respect for me. I appreciate the disciple who pay his respect by following my teachings (Prathipaththi Pooja)."


However most people have forgotten these words of the Blessed One.