why do i have to hold the lever down

You shouldn't need to, except for solids or large deposits. You have a dual flush toilet, though it's likely not sold or marketed as such. A press and release initiates a very quick and short flush that barely empties the bowl, for liquids only. A press and hold allows for a full tank emptying and double wash of the bowl. They can be annoying, but frankly, the holding for a full flush each time is actually better for your plumbing's longevity.