Because of
diabetes.
I am a serious coffee drinker too - I work at a cafe and have access to aaaaaall sorts of sweet stuff
My father had his coffee like you, too, and it brought him very close to the edge. He had no choice but to cut down - so he drank less coffee. I opted to change my sugar intake gradually to zero. My excuse is snoberry - you can really taste the uniqueness of the coffee, the distinctness of its roast and its origins. (I also spend 8 bucks for a pound of Costa Rican fair trade coffee. I love it and it makes my day, the wallet ouchies are really worth it.)
You could make coffee milder - I drink a lot of less-strong-but-delicious coffee, and have it black.
You could make a sort of caffe latte with skim milk. I have an easy shmeazy stove espresso maker and a metal milk frother that lets me heat milk on the stove. The milk sweetens it (a bit) and offers me calcium and protein that I wouldn't otherwise have.
Make yourself a coffee protein shake? You could refridgerate cold coffee, use a bit of splenda.