I thought I remember a blog post by them explaining how it's impossible to catch up with Google results due to the control they have and money involved, so they have their own indexing service that also pulls from others that they pay for access to (other than Google).

I may be wrong but that's how I've understood Kagi's results as I've used it for the last 2 years...

Edit: Found the article

https://blog.kagi.com/waiting-dawn-search