How single responsibility principle avoid code smell in this scenario?

I'm new to Design Patterns, I know the purpose of single responsibility principle, but not 100% sure how it can avoid lots of tiny changes. Below is my example:

//very crude implementation
public class Journal
{
    private readonly List<string> entries = new List<string>();
    private static int count = 0;

    public void AddEntry(string text)
    {
       entries.Add($"{++count}: {text}");
    }

    public void RemoveEntry(int index)
    {
       entries.RemoveAt(index);
       count--;
    }

    public void SaveToDisk(string filename)
    {
       File.WriteAllText(filename, ToString());
    }
}

I know the SaveToDisk method should not be included in the class, it should be a dedicated class, like PersistenceManager to handle the file saving.

But why can't I keep the SaveToDisk() method in Journal class? if there is any new requirements such as Save the Journal to cloud, then I just add a new method SaveToCloud(), and any dependent client classes can use SaveToCloud(), the only modification I need to make is adding SaveToCloud() in Journal class, which is totally fine?