This isn't entirely true, because they use more than one search index.

The other search indexes are largely negligible in comparison: [0]

> This is not a competitive market. It is a monopoly with a distant second place.

> The search index is irreplaceable infrastructure. Building a comparable one from scratch is like building a parallel national railroad. Microsoft spent roughly $100 billion over 20 years on Bing and still holds single-digit share. If Microsoft cannot close the gap, no startup can do it alone.

[0]: https://blog.kagi.com/waiting-dawn-search