What do you think its niche is?

Very large "single product" services, the focus being on "very large". It would also be relevant in the cases where your product is made up of a large number of micro-services, though if you have more than 50 services to support your main product I'd be interested in knowing why you have that many services. There might be completely sane reasons, but it is a special case.

Mostly a question of scale to me, I'd guess that the majority (80-90%) of people running Kubernetes don't have large enough scale that it makes sense to take on the extra complexity. Most Kubernetes installations I've seen runs on VMs, three for control plane and 2 - 5 for worker node and I don't think the extra layer is a good trade off for a "better" deployment tool.

If you do use Kubernetes as a deployment tool, then I can certainly understand that. It is a reasonably well-known, and somewhat standardised interface and there's not a lot of good alternatives for VMs and bare metal. Personally I'd just much rather see better deployment tools being developed, rather than just picking Kubernetes because Helm charts are a thing.

You'd also need to have a rather dynamic workload, in the sense that some of your services is need a lot of capacity at one point in time, while other need the capacity at another time. If you have constant load, then why?

It's like Oracle's Exadata servers, it's a product that has its place, but the list of potential buyers isn't that long.