I didn't even think about it till I was looking at a pack about 6 months ago...I'd replaced eating snacks with chewing entire packs of sugarless gum. I was so mad when I realized that there were calories that I didn't know about.
I'll never know why sugar-free sum has calories yet I can drink a swimming pool full of diet coke and not ingest a single calorie!
It's because they use sugar alcohols for the texture and they have from 1 to 3 calories per gram.
Sugar cane works and sugar alcohols work but no-cal sugar SUBSITITUTES (like aspartame, sucraloase, acesuflame and cyclamate) DON'T have the waxy texture that makes for a gum.
It's just the way of the world.