google has been apple's greatest competitor for a while. apple has > $160B in cash. mobile bing is comparable to mobile google. the strategic value of weakening

google has been apple's greatest competitor for a while. apple has > $160B in cash. mobile bing is comparable to mobile google. the strategic value of weakening google seems to far outweigh the financial value of defaulting to google search (assuming google is willing to outbid microsoft). so why hasn't apple defaulted to bing yet, and when will it?