perhaps something like "Warum mag Man alle Katzen?" I feel like "Why like all cats" in English is a short form of a question that implies "Why does one like all cats?" or "Why should one like all cats?", which might have to be spelled out explicitly in German.
Apparently there is no real difference, one theory states that "the German question word warum asks for the REASON,[and] wieso for the CAUSE". However, from what I've seen online, not even the native speakers know the difference.
.....I also thought that the "alle" went with the "cats" to say "all cats" .....I think it is just a matter of seeing the sentence and plugging in how it looks in English...word for word.....why + like + all + cats