It's based on Google and Bing.

It takes hundreds of millions of engineering, server, work time and internet cost to crawl and index the whole web.

Only Google, Bing (Microsoft) and Yandex have done it.

Everybody else is now copies of the above, with some difference in results ranking. Nobody is running their own 24/7 crawling robots indexing the internet.

Yandex is still the least censored search enginer results, for almost anything (except for heavily Russian critical information).