If you use marketing it will increase. As the years progress too, the demand increases. As you are looking replace aircraft, typically an upgage in size or frequency will be in order. The game has always done this will real life demand and with the old false demand.
The game wants you to right size the plane for the route. 3 to 6 or over 10 flights a day will keep you in the green. It is something that should be looked at if the game is ever updated.
Typically I am using both. Typically using the 777 for the longer routes because it is faster than 330. My typical layout is the same in the game for both aircraft.
These simulations move too fast compared to real time to account for these little ripples There are other factors that should be adjusted first: IFEs, high utilizations, and aged aircraft.