Tap Forms has a built-in backup mechanism which will let you backup the entire database at once. You can access the backup function on the Tools screen and tap the Backup & Restore function. There are instructions there which tell you how to perform a backup to your PC.
I guess it might be handy for some people to have a CSV export of all their forms at once. This is something that might go into a future version. If you’d like to request that feature “officially”, please submit it to my feedback site at http://feedback.tapforms.com