WD Backup software - extremely large back up

I was using WD smartware to back up my PC. I backed it up to a 2TB WD drive. I noticed that this was getting full so I invested in a 6TB drive. To my surprise this was not supported by WD Smartware but an alternative WD Backup was offered.

I have been using WD backup for one month and now the 6TB drive (which is only used for the backup) is 95% full.

He are the numbers;
The C: drive I am backing up has 388 GB of data.
The back up on the 6TB drive consists of 388GB in the back up and 4.67TB in the history.
I back up every hour.
What’s going on?
Is WD Backup WD’s way of making me buy ever bigger drives?
Can someone suggest a better alternative to WD backup?
I thought I had this issue fixed by deleting some unwanted files but this in the end did not fix the issue.
Nothing seems to be duplicating in the back so what’s going on?