If this doesn't quite make sense, maybe we need to put the final piece in the puzzle. It stands for compact disc recorder. Philips and Sony are each about to announce a compact disc recording system. They may be collaborating on a joint system or they may be working on separate formats, but it's clear that they are both close to an announcement. A recordable CD if it works properly would almost certainly put tape out of business.
CDs are cheaper, more durable and easier for a recording device to work with.
There you have it. In this scenario, Sony makes a splash in Japan with DAT while making money worldwide with CDs. It sure makes sense to me.