Bing seems to lack mobile search. While there search page is optimized for mobile, they don't seem to rank mobile differently. That alone could be a deal killer for the Japanese market.

For instance, they're still operating geocities.jp, whereas the .com (and all the others) has closed, and in general they seem to be able to make a go of things where the .com version falters.

Also there's some bullcrap at the end. Most of the time in yahoo history the "heart" of it was done by a 3rd party company,e.g. google. Which became a company we know only after yahoo used them as their search engine long ago