Why does backup exclude certain Windows folders by default

Why does the backup set EXCLUDE certain Windows folders by default (e.g. C:\Program Data\, etc.)?

That's understandable, and I greatly appreciate your prompt and concise response.

Turn on Norton backup from Settings window
https://support.norton.com/sp/en/us/norton-360/current/solutions/v7821374

Get started using Norton Cloud Backup 
https://support.norton.com/sp/en/us/norton-360/current/solutions/v19213795

Delete backup set and files from Norton backup 
https://support.norton.com/sp/en/us/home/current/solutions/v19828921

Manage backup files on Norton Backup Drive 
https://support.norton.com/sp/en/us/home/current/solutions/v19828933

Modify settings for or rename your Norton Backup sets 
https://support.norton.com/sp/en/us/norton-360/current/solutions/v19828922

Add or exclude files and folders in your backup sets 
https://support.norton.com/sp/en/us/norton-360/current/solutions/v20534334

View or change the default file types or file extensions that Norton includes in backups
https://support.norton.com/sp/en/us/norton-360/current/solutions/v7344814

Restore pictures, music, or other important files from Norton backup sets 
https://support.norton.com/sp/en/us/norton-360/current/solutions/v6958542

Choose the location of the files to be restored before running Norton Backup 
https://support.norton.com/sp/en/us/norton-360/current/solutions/v7927242

Fix problems with storage space in Cloud Backup
https://support.norton.com/sp/en/us/home/current/solutions/v128450551

Norton video tutorials - Backup and Restore

Learn about online backup and how to activate it. You can use the videos in this section to learn how to create a backup set, run a backup, restore your data, and purchase additional storage space in case you run out of the allocated online storage space.

  • Activate Cloud Backup
  • Set up and run Cloud Backup
  • Restore files from a backup set
  • Free up space in Secure Cloud Storage

https://support.norton.com/sp/en/us/home/current/solutions/v102698236

Norton is providing an example (recommendation).  You may include/exclude those items.  They'll take up space.  I'll remove those items from the list and create new sets with my backup preferences.  Cloud Backup is for user created personal files.  Norton lets you back up different file types, like picture, music, or video files, to your backup sets.   Backup Set DefaultSet is an example (suggestion - starting point).  You may add or exclude files and folders.  You may create new set/s. 

for example: my backup preferences

Cloud Backup stores and protect important files and documents as a preventative measure to data loss due to hard drive failures, stolen devices and even ransomware.
Cloud Backup backs up personal files. 
Cloud Backup does not create - store System Image Backups. 
Cloud Backup is not a disk imaging solution. 
for example: https://www.macrium.com/reflectfree