Actually, it can. It's not important for the definition of a monopoly, if people are forced by external, unintentional circumstances to use a certain product (like it is the case with Windows or Office).
In several major countries Google has >90% market share. Their global dominance is so strong they coined a verb of their own, and if you ask any random person in any random place on earth, chances are they know and use Google every day and haven't heard of other search engines.
Also don't forget that Google doesn't just have a monopoly among users but also among ad space sellers. In that respect their stranglehold is as strong as Microsoft's. Most companies are forced to buy Google ads if they want to get noticed, just because Google is so ubiquitous.
You are right, users could switch to another search engine with a simple mouse click, but chances are they won't. Most people wouldn't even notice worse or biased results, because for them Google results ARE the internet. They would never even suspect wrongdoing.
Just look how long it took other, far better browsers to overtake IE. People are lazy.