It's actually between $8-12 billion now. [1]
> Yahoo & MSFT's experience as 2nd place in that market was working very hard and earning $0 profits.
This is an exaggeration though. MSFT made nearly $8 billion in revenue last year from search (mostly Bing), and the business has naturally high margins so it would be extremely surprising if it was unprofitable on an operating basis. [2] The reality is that search is so huge that it's worth competing in, even if the incumbent has 30X your market share.
[1] https://twitter.com/jowens510/status/1428416856038072321