Why would Microsoft want to sell, and why would Apple want to buy?

As I understood it, the point of Bing was for Microsoft to have a good-enough search engine so that Windows users would accept the default. They could leverage that the way Google does, to lock users into a whole ecosystem of tools.

If that was right, Apple would have no interest in buying it. They can surely do their own search engine.

And Microsoft wouldn't want to sell it. They'd need something to anchor their web ecosystem. Bing is a brand more than a technology.

I don't doubt that TFA is right that they did try to sell it. But I have no idea why.