@PhilipKing @thibaultmol Kagi user here: Because there's more features tied to your account.

Two examples:
There's for example 'Search Lenses', which limit searches to certain websites (multiple sites, so more powerful than site:example.com).

There's also a way to hide, lower, raise & pin websites in search results. This also requires your account.

Having a separate trust service for the payment part, would still require an account in these cases.