If you're doing any modern architecture with microservices using containers, you're primarily doing stateless things (even if it's your web frontend) and pushing the state off to somewhere like Redis/memcached/database.

You basically implied that web frontends don't run in a load-balanced multi-replica set up, which is not true.

Similarly from what you said one might think people don't deploy web frontends to Kubernetes (where containers come and go all the time as they're ephemeral, due to events like crashes, autoscaling), which is also not true.

If you’re writing anything that scales (i.e. has multiple replicas), then you actually store any significant state wrt logins/sessions on your app and you push it out to an external storage. Most web frameworks offer libraries or middleware that let you persist this "state" in external storage.