Just to add to my theory that cc uses more here’s a bit more evidence
And just to add to the previous comment there are a lot of motorways that are not flat! try driving up north ! I can bet there’s more motorway that’s not flat!
This explains it very well
And by the way iv got cc
Here comes the science bit
Advantages and disadvantages
Some of those advantages include:
Its usefulness for long drives across sparsely populated roads. This usually results in better fuel efficiency.
Some drivers use it to avoid unconsciously violating speed limits. A driver who otherwise tends to unconsciously increase speed over the course of a highway journey may avoid a speeding ticket. Such drivers should note, however, that a cruise control may go over its setting on a downhill which is steep enough to accelerate with an idling engine.
However, cruise control can also lead to accidents due to several factors, such as:
The lack of need to maintain constant pedal pressure, which can
help lead to accidents caused by highway hypnosis or incapacitated drivers; future systems may include a dead man's switch to avoid this.
When used during inclement weather or while driving on wet or snow- and/or ice-covered roads, the vehicle could go into a skid (although this may be somewhat mitigated by cars equipped with Electronic Stability Control). Stepping on the brake — such as to disengage the cruise control — often results in the driver losing control of the vehicle.
Driving over "rolling" terrain, with gentle up and down portions, can usually be done more economically (using less fuel) by a skilled driver viewing the approaching terrain, by maintaining a relatively constant throttle position and allowing the vehicle to accelerate on the downgrades and decelerate on upgrades, while reducing power when cresting a rise and adding a bit before an upgrade is reached. Cruise control will tend to overthrottle on the upgrades and retard on the downgrades, wasting the energy storage capabilities available from the inertia of the vehicle. The inefficiencies from cruise control can be even greater relative to skilled driving in hybrid vehicles.
Many countries establish that it is illegal to drive within city limits with the cruise control feature activated.[citation needed]
Now that last paragraph backs my argument very well.