Market share should be relative, so if there was a stark decline in search bing would have declined close to as much as Google. Unless this is some other measure erroneously labeled as market share
.
Like hyping how your market share went UP. But you lost customers, sales were actually DOWN. Just the other guy lost more. So your market share went up.
I've been in companies that had bad sales, and they super hyped how market share had gone up like we were winning. But the entire market was shrinking enough that total sales had gone down.