Increasing storage when deleting Apps.

Are you positive the two things are related? As stated earlier, deleting an app should delete the data too. See if this document provides any suggestions, particularly the section "Use your device to check its storage":

How to check the storage on your iPhone, iPad, and iPod touch - Apple Support

Sometimes it is worth restarting a device to clear up unusual issues, and it can't hurt.

Depending on the app, it will take up a certain amount of storage on the iPad. When an app is deleted, the storage it takes up is deleted with it, causing you to have more storage after deleting apps.