Re-enabling plugin reverts options to defaults

If you deactivate then re-activate the plugin, the options reset to defaults.

In the set_default_values() method in the activation hook I see:
update_option('ip2location_redirection_api_key', ''); which will always update the value if it has already been added.

Is there a reason to not set default values with add_option() instead? This way existing options/settings will not be updated. Like:

if (!get_option('ip2location_redirection_api_key')) {
  add_option('ip2location_redirection_api_key', '');
}