The reasons FaunaDB fits serverless like a glove can be boiled down to a few points: pay-as-you-go, database security awareness and object level access control, hierarchical multi tenancy with quality of service management. Running on multiple clouds makes the Serverless model more acceptable for risk averse enterprises, and complements multi-cloud serverless FaaS execution environments nicely.
There's more to say, check out this post on the blog: https://fauna.com/blog/serverless-cloud-database and https://fauna.com/blog/escape-the-cloud-database-trap-with-s...