Makes more sense. But it is easy to replace it with another giphy. Especially when there is privacy reason.
Question os: How many will switch it out? Giphy has a big collection of images and works ... swapping is effort and brings different (unexpected?) results.
Create a proxy that exfiltrates their active database while providing anonymity.
Again, a small number of people might do that, if one gets too large by chance Giphy/Facebook will attempt to block them. Most users and integrations will be kept. As people stay on WhatsApp etc.
For $400m?
Eyeballs. It's used casually by many millions of people daily. That's all that's needed to justify price.