Hello, In Salesforce, Custom Settings are a type of customizable, persistent data storage that allows you to create custom data sets. They are similar to custom objects but have some distinct characteristics and limitations. One of the limitations of Custom Settings is that they cannot be deployed using standard deployment methods like Change Sets or Metadata API. The reason for this limitation is that Custom Settings are considered to be part of the organization's configuration and not its metadata. Configuration data, including Custom Settings, is expected to be manually set up in each Salesforce org to maintain the integrity of the data and prevent unintended changes during deployments. This approach ensures that the custom data remains specific to each org and can be modified without affecting other orgs.
The reason for this limitation is that Custom Settings are considered to be part of the organization's configuration and not its metadata. Configuration data, including Custom Settings, is expected to be manually set up in each Salesforce org to maintain the integrity of the data and prevent unintended changes during deployments. This approach ensures that the custom data remains specific to each org and can be modified without affecting other orgs.
I came across a discussion which has been asnwered by the original inventor and lead developer for custom metadata types of salesforce .
Requesting you to go through it once for your understanding -> https://salesforce.stackexchange.com/questions/74049/what-is-the-difference-between-custom-settings-and-custom-metadata-types
https://salesforce.stackexchange.com/questions/282431/custom-setting-deployment
Hope this helps !
Thank you.