Wasm also offers incredible density characteristics. The same application hosted in a container has a much larger footprint than the Wasm equivalent, ~hundreds of MBs to GBs compared to a typical Wasm app that is typically <10MBs and often KBs. Wasm is based around a linear memory model such that it supports binpacking by the runtime. Where a system may be able to run hundreds of containers, thousands of Wasm instances can be run by a single Wasm runtime.
The typical cost savings for using a Wasm-based serverless platform vs a container-based one is significant. This is dependent on the language and workload, but I generally expect +30% efficiency.
Containers are not secure by default and are generally not considered an appropriate sandbox. Wasm was designed to run in the web where sandboxability is a critical requirement and first principle of the design. For serverless, this means a single Wasm host may be multi-tenant. This is why Fastly, Shopify, and Cloudflare use Wasm for serverless workloads ($$$ + safety).