It is monstrously hard to offer alternatives. The barrier to entry is the massive engineering effort to compete.
Google is not just a search engine. It is an email server and client, a calendar, an online office suite, a cloud provider, a mobile platform, and I can go on listing things to fill up several pages of what Google is.
Even if DuckDuckGo is a better search engine, it offers 1% of the feature set and can't compete. The engineering effort needed for it to compete effectively is astronomical. Imagine what it would take to build out all of those Google services that are tightly integrated and not just build them out (like Microsoft), but build them out well. That is the barrier to entry.