I'd argue if you live in first world, earn a living from tech, even if you don't care whether you pay for things vs. be tracked, it's worth the subscription, in the sense of, it's enough better to be worth paying for as a better tool, not just because there's no gaming of the SERPs above the fold. The Lenses are impressive, but it's not just that, the results are what one used to appreciate from web search. After getting used to the quality, the lower quality of Google or the Bing derivatives like DDG will frustrate you.
If you dislike adtech or value privacy, it's worth the subscription, because there are no ads and no tracking. (Also, unlike neeva, to which I also subscribe, it's not an ad-alternative model from former ad-tech people.)
Globally, I can easily see enough users sign up to sustain the small team. Their blog post [0] mentiones they calculate they need 25,000 subscribers to sustain themselves.
(I'm a paying customer, FWIW).
[0] https://blog.kagi.com/status-update-first-three-months#futur...
But highly unlikely to be better enough to justify paying a subscription for it (for most people, anyway), so it's always going to be confined to a small niche of users.