In part, and I know this is 'blame the victim' I think shareholders truly are dumb, if they thought it was AGI and some god given uplift to the cloud-mind: it was never going to do what they wanted, and rather than 'Google erased' I'd say google communications/marketing erased: they really didn't prepare this package for release well.
Too much infeasible community expectations on something which was incapable of doing what they wanted.
No matter what the $100b is gone. I'd say the buyers at the bottom picked up a bargain btw.
Maybe most consumers ultimately core more about the improved search capacity of Bing than that it might say weird or offensive stuff in some prompt-engineered worse cases. Plus it doesn't need to be 100% accurate, just no less accurate than the average person's SEO-laden Google search results.
Because Bing isn't a material profit generator for Microsoft right now, AI search is a lottery ticket for Microsoft while Google is playing defense for their main revenue stream.