You are doing nothing wrong......that is just the nature of ornamental alliums. With the majority of species and cultivars, by the time the flowers appear, the foliage looks like crap. The trick is to plant them in amongst other, more leafy perennials to disguise the drying and dead leaves.

One of the few species that can maintain attractive foliage throughout the season is Allium karataviense Ivory Queen. But it also does not have a very imposing flower compared to those like Purple Sensation, etc.

Because thats the normal course of things with Alliums.

Thanks @gardengal48 and wh431. I will move the alliums to better spots. I feel less stressed everytime I see them :)