You can remember the meaning of 为什么 with this easy mnemonic:
A man and a woman had dated for eight years and the man decided to propose. Why? Because it seemed the natural thing to do (为) for the future. Their friends have also asked what (什) (么) has taken them so long.
Using mnemonics to remember the meaning of Chinese characters like can have an enormous impact on how long to learn Mandarin it takes.