You can't go to 700c without switching the wheels. And often that isn't an option either because of things like canti brake boss height, and/or overall fork clearance. In any case even if you can make the switch, it will raise the BB height another 3/4", which woin't be desirable in a cruiser.
However there is a vast selection of cruiser or city/slick road tires in the 26" size. After all 26" was the cruiser wheel size long before mtn bikes were invented.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.