I’d like to validate that the two Malay why-words are interchangeable to my mind.
Here are some telling findings:
1. Kenapa perempuan mudah menangis?
(Why women cry easily? asking for a reason)
2. Kenapa komputer saya mati saat loading windows?
(Why my computer dies when loading windows? asking for a reason)
3. Kenapa michael jackson..?
(Why Michael Jackson….asking for a reason)
A. MENGAPA SAYA MASUK AGAMA ISLAM
(Why I become a muslim? Providing a reason)
B. Mengapa akses firefox saya lambat?
(Why is my access to firefox slow? Asking for a reason)
C. Mengapa King Kong digunakan untuk nama Kera atau Monyet Raksasa?
(Why is King Kong used to name Ape or Giant Monkey? Asking for a reason) http://answers.yahoo.com/question/index?qid=20071119083301AAy8dcM
Preempting ancient skepticism that the above are online examples,
I ran through Jendela Bahasa (EPB 2003), the Malay textbooks for secondary 2Express.
All the Why-questions are constructed with Mengapa in Book 2(B) containing comprehension 9 to 16.
Nowhere was Kenapa noticeable.
My preliminary conclusion: kenapa is mengapa’s informal incarnation (why).