Why does tarter tend to form back on your teeth after a scaling even if you are brushing twice daily?

I had to get a scaling done on my teeth in 2005. I have been brushing, flossing, and swoshing faithfully in the morning and before bed ever since. After I brushed my teeth yesterday evening , I noticed tarter has formed again in the back of my upper teeth. What extra steps can I take to prevent having this procedure done every few years?