iCloud Backup "Next Backup Size" still TOO BIG?!

I use the iPhone 11 Pro Max, fully updated to public iOS 14.2. I was about to check my backup, because I like to see what goes in my phone from time to time. I like to clear unnecessary stuff. So I was checking the backup and noticed that my "Next Backup Size" has estimated 5.72GB. It should be impossible given that I have excluded every big file that even takes over 200 MB. I deleted old iMessages attachments. My WhatsApp Messenger says it only has covered over 25.2 MB on my phone, and around 100MB on cloud, which barely can take over. My notes takes in 208 MB. In total it should be less than 1.5 GB. But the "Next Backup Size" says it is over 5.72 GB.

I just want to know why it would say that given that I have deselected all big sized application, and deleted unnecessary files in iOS Files.