Google won because they started early and had the right algorithm. Back in 1998, Google's PageRank was an innovative algorithm that calculated relevance based on counting backlinks instead of parsing the word counts in embedded HTML text like other search engines. This made Google way better than any other available search engine back then (Lycos, Yahoo, AltaVista, etc.), and within weeks, everyone was switching to Google.
A successful Google competitor just needs to be way better than what’s currently available. Nobody seems to have The next big idea for a better search engine yet.
Google then had the scale to grow with the internet. The high cost of maintaining a fresh index, and the decision by many large webpages to block most crawlers make it hard to start a new general-purpose search engine today. Google and Bing are currently the only search engines that maintain their own comprehensive webpage index.
Google pays Apple around $10bn a year to be the default search engine on Apple devices. They pay Mozilla a significant percentage of Mozilla's revenue to be the default in Firefox. Obviously Google is the default in Chrome. On Android, Google is deeply integrated into the OS. You can't compete with that by building a better search engine, even if you had the infrastructure and the capital. DDG and other competitors wrote about the issue of choosing your default search engine. Without laws or regulations, not much will change in this aspect.
By making its products and services work together, Google has been able to keep its customers locked in. This has been a key driver of Google's growth, making it difficult for competitors to replicate.
Google no longer producing high quality search results in significant categories
Ask HN: Why isn't there a Google competitor emerging?