I mostly think of serverless as abstracting the actual way things run more and having a more specific contract than "exposes a port". I imagine this allows for

I mostly think of serverless as abstracting the actual way things run more and having a more specific contract than "exposes a port". I imagine this allows for deeper integrations and features like handling cold starts. It is difficult to mitigate a lot of these problems without a good contract/interface that allows it, and an arbitrary container doesn't really let you do that. It's similar to buildpacks on Heroku. How are they all that different from containers? Well, Heroku runs buildpacks in their own container system, so they're not much different, but Heroku can more easily control updates to packages and the base OS of their containers by not allowing you to run arbitrary container images. In the end, I think of these as higher level abstractions, often building upon containers, but not allowing as much flexibility so the "serverless runtime" can optimize more things.