I grew up in Salt Lake City. As a teenager, I rode 250 miles a week. Rode the canyons every day, loving the up as much or more than the down (I've got a climber's build).
Eventually, I ended up in the midwest (Madison, WI) for grad school. In 8 years there, I rode a maximum of 500 miles total.
Since I've been in Bonn (where there are things that almost qualify as mountains and are certainly very respectible hills), I am back to logging significant kilometers.
Nothing against the flatlands in principle. I liked Madison for many reasons. But the flats just don't get me on the bike.