"Why not?"

The question, 'why not?' has been stumping me today.  Big Brother has been weekly rotating some challenging words into his vocabulary.  2 weeks ago the favored phrase was 'I can't' and I am learning to respond to that with 'I would like you to try' - that seems to be working or at least deflecting some of the annoyance of those words for me.  Today, his new 'saying' is 'why not' (we've been through just 'why' but this is different). He does not always use it in the right context so it leads to ridiculous conversations.  The washing machine repair man was here today and Big Brother asked me 'why not was he fixing the machine' - hmm - and then he asked 'why not was he wearing a hat' - he wasn't wearing a hat so if he had flipped a few words around it would have worked but ... :) Oh the challenges of the English language.