My guess is he was a great option buy. A fantastic player who wanted to step up. And we having the funds to make it happen.
Besides, considering Kompany consistent injury situation. It was a no brainer. Not to mention, even when Komps played last year, he wasn't very good for a good portion of the season.
Thus, with an injury prone captain, an aging vet, an an up and down big money signing, it was clear we needed another CB. And if they all pan out, we'll have 3 studs. But more likely than not, the sense was Komps wouldn't hold up for a whole season.
Couldn't be happier about the signing.