From their desire to representatively test before they deploy to production?

Doing stuff at scale doesn’t suddenly mean you skip testing.

And just because they host stuff themselves doesn’t mean they couldn’t run on the cloud if they needed to.

Cloudflare infra costs are probably 300 mil+ usd. Their gaap profit is negative, their non gaap income is less than their infra expenses. Can you imagine how much they would have to charge more or spend more if they had to duplicate or simulate their production environment in staging and for each of the 100s deployments they probably do a day?

Their main cost of revenue is these infra costs.