The capital requirements and regulatory barriers to start an insurer are extremely high.

There are lots of small insurers at least.

Multiple resources on the internet put the startup costs at $500K or less. That's not much more than fast food or other high touch retail startups by comparison.

There are certainly a few steps on the learning curve but it's mostly high school and undergraduate math that is needed. That puts it out of reach for some but the field is pretty flat once you get there, is my perspective having considered and opted against getting into it.

In other words, there's no moat in insurance.