"why" can be compared to an old Latin form qui, an ablative form, meaning how. Today "why" is used as a question word to ask the reason or purpose of something. This use might be explained from a formula such as "How does it come that ...".

Understanding the Context

If you meet an old friend of yours, whom you never expected to meet in town, you can express your surprise by saying: Why, it's Jim! This why in the ... The question is: why did the English adapt the name pineapple from Spanish (which originally meant pinecone in English) while most European countries eventually adapted the name ananas, which came from the Tupi word nanas (also meaning pineapple). So, why does she ever tweet with standard capitalization (and do so quite randomly and quite frequently)?

Key Insights

In contrast to the other answers, my answer (typing in only lower case is simply faster) explains the above tweets quite simply: