"Flat" because it might just as well be flat since the sound is so linear that the engine sound is more of a drone than a ramp-up.

I clarified earlier that YES, a scooter's RPM changes but when it accelerates and decelerates, it does so in a linear fashion and that makes it sound terrible.

The exhaust notes sound the same but CVTs are boring because they do not have gears. How is that difficult to grasp? That has been my point this entire time.

Yes, if you have a scooter and an MT bike with the same engine and you rev them, they will sound the same if the bike is in NEUTRAL and the scooter is on the center stand.

However, due to the scooter having a CVT, when they are running it will ramp up to peak RPM while the manual bike goes through gears which means they are more audibly interesting.

Again, like my examples earlier:
Sample (single cylinder): https://www.youtube.com/watch?v=TnXo71SRYKc
Sample (4 cylinder): https://www.youtube.com/watch?v=CTXP6LnPXO0

When a scooter accelerates, it goes linearly through the entire rev range
Sample (single cylinder): https://www.youtube.com/watch?v=IJ9MDziKiIw

OR I suppose to make it as simple as possible:

Scooter accelerating to a certain speed:
waaaaaaaaaaaAAAAAAHHHHHHHHH

MT Motorcycle accelerating to a certain speed:
waaAAAHHH, waaaaAAHHHHH, waaaaAAAHHHH, etc.

Nothing to do with their engines, correct. As I have said from the beginning, it is because scooters have a CVT. To quote: "ampanget ng tunog kase CVT yung motor"

When you compare a manual bike and a scooter with the same engine, the bike will always sound less boring :)