It's a consistent, powerful abstraction for a cluster of Linux machines, which allows you to treat machines as one (with fault tolerance to individual machine failures).
It makes apps easier to design, run and scale. A Kubernetes single node install on your laptop behaves exactly the same as a cluster of 20 dedicated servers, or 5 VMs on a cloud provider.
I plan on moving most of my apps to it, so I can spend a lot less time doing operations. Servers stop being special, there's no such thing as "the database runs on this server", Kubernetes decides and manages that for you.
There are likely many possible business models, such as running a wordpress install (mysql / php / nginx all isolated per client) for each client easily.