It is that large probably because it originally wrote data there before you switched it to a different drive. Bitcoin Core will not delete data from previous datadirs, it does not know about them so it cannot do so. If you don't think you need that data, you can just delete the folder.
Definitely do not delete the entire Roaming directory though as that contains files for many other applications. I recommend that you enable Hidden folders in Windows Explorer if they are not already enabled as its possible the other files taking up the space are located within a hidden directory.
