Here's why:
* "Why" is usually a question word. It's not a common word ending for nouns or adjectives.
* "Why" is rarely used as a suffix. There are very few words formed by adding "why" to a base word.
Therefore, there's no established rule for adding suffixes to words ending in "why" because such situations are uncommon.
If you encounter a word ending in "why," it's best to check a dictionary or reliable language resource to see if there are any specific rules or exceptions that apply.