Why one page website is not good for SEO?

One-page websites are not good for SEO because they are difficult to crawl and index. Google and other search engines use algorithms to crawl and index websites. These algorithms are designed to crawl and index websites with multiple pages. One-page websites are often not crawled and indexed properly, which can lead to poor search engine visibility and rankings. Additionally, one-page websites generally have less content than multi-page websites. This can also impact SEO, as website content is one of the key factors that search engines use to determine rankings.