Stores reject labels for a variety of reasons. The most common reasons are listed below -
Genre Not Suitable - Labels are commonly rejected because your genre of music does not fit the customer base or profile of that particular store.
Downsizing - From time to time some stores remove labels in order to free up hard drive space for other labels that they feel will sell better on their store.
Poor Sales - Your label may be removed if your sales are poor. Similar to downsizing above - they do this to keep their servers clean and also to keep their store listings clean.
Not Established Enough - If you are a new label you may well find your label is rejected because your label has not yet built up a proven track record of releases and sales.
To find out exactly why your label was rejected from a particular store please contract LabelWorx support.