Here's my experience with scooters and belts.
Kymco Super 8 150. 33,400 miles with no belt or roller issues. I ran that scooter very hard.
Aprilia Sport City 250. 25,000 miles. Replaced the belt and rollers every 12,500 miles. Belts and rollers looked fine. I ran that scooter pretty hard and often ran at high speed on the highway.
Yamaha Majesty. I replaced the belt and rollers at 18,000 miles and they looked fine. At 29,400 miles now. I'll probably replace the belt and rollers around 33K.
Kymco Like 150i. I ride it a lot at 50-60 MPH. Belts broke at 10K and then 7.3K later. Rollers looked really bad.
Yamaha Smax. Didn't own it long enough to replace the belt or rollers.
So why have I had issues with the Like and not the others? I don't know but it's both the belt and rollers that have been wearing out to fast. I inspected the pulleys looking for rough spots but didn't see anything. Maybe the belts and rollers are just lower quality? Maybe the airflow isn't as good and it's the heat. Maybe the worn out rollers put stress on the belt? I don't run it any harder than I did the Super 8 but it does have a bit more power. Maybe I should try sliders.
I think that competitors in the Scooter Cannonball often carry spare belts and rollers. I have heard other people have issues with rollers flat spotting but I haven't had that issue except for the Like.