I wouldn't doubt that skimping on the cinnamon is a cost-saving measure. And it's easier to just drizzle some corn syrup on the thing than to give it a proper frosting.
Also, it's a truism that the Taiwanese tend to like their drinks much sweeter than Westerners and their pastries drier and less sweet. I think it's telling that Taiwanese usually call pastries "bread," as it's kind of all the same to them. The pastries aren't sweet enough (and don't have enough butter...or even real butter at all), and the bread is too sweet.
Then again, it seems like it's harder to get a decent cinnamon roll in the U.S. these days. I blame Cinnabon.