Anycast but for egress

(Unsure if this is the right forum to ask this question, but here goes:)

From what I understand, IP Anycast can be used to steer traffic into a server that's close to the client.

I am curious if anyone here has/encountered a setup where they use anycast IP on their gateways... to have a predictable egress IP for their traffic, regardless of where they are located? For example, a search engine crawler could in principle have the same IP advertised all over the world, but it looks like they don't... I wonder why? -- Vimal