There could be several reasons why a nested dictionary is incorrectly populating all top-level key-value pairs with the same values. Here are a few things you can check:

1. Make sure you are using the correct syntax: When creating a nested dictionary, make sure you are using the correct syntax and properly separating the keys and values. For example:

nested_dict = { "key1": { "subkey1": "value1", "subkey2": "value2" }, "key2": { "subkey1": "value3", "subkey2": "value4" } }

2. Check if you are overwriting the values: Make sure you are not accidentally overwriting the values of the nested dictionary. For example, if you are using a loop to populate the dictionary, make sure you are not using the same variable names for the keys and values in each iteration.
3. Check if you are using the correct keys: Make sure you are using the correct keys to access the values in the nested dictionary. If you are using the wrong keys, you may get the same values for all the top-level key-value pairs.
4. Debug your code: If you are still having trouble, try debugging your code to identify the cause of the issue. You can use print statements to check the values of the variables at different points in your code, or use a debugger to step through the code and identify where the problem is occurring.

By following these steps, you can hopefully identify and fix the issue with your nested dictionary.