Because it's a paid service? That's the entire point.
And that also enables tons of user-centric features they talked about, starting with the earliest ones and my favorites: being able to uprank and downrank domains (like, "ban pinterest", "pin Wikipedia", "downrank w3schools", "uprank cppreference", etc.), and adding rewrite rules to results (like "reddit.com" -> "old.reddit.com"). Both of these are personalizations tied to your account, so they're active on any device as long as you're logged in.
They've added more cool stuff since, but these two alone were what has kept me a paying customer for the past years.
Google knows what you search, even in "incognito" mode, and even when you're logged out. They correlate your IP address with your search profile and use everything you search for in your ad profile.
Kagi does not track search history, period. There's no history attached to your account even if you wanted it. The login is purely for authentication.
And that also enables tons of user-centric features they talked about, starting with the earliest ones and my favorites: being able to uprank and downrank domains (like, "ban pinterest", "pin Wikipedia", "downrank w3schools", "uprank cppreference", etc.), and adding rewrite rules to results (like "reddit.com" -> "old.reddit.com"). Both of these are personalizations tied to your account, so they're active on any device as long as you're logged in.
They've added more cool stuff since, but these two alone were what has kept me a paying customer for the past years.