That might work in most cases; however, it is also important to consider what would happen if someone searched for multiple words. Some maps will contain all the words, some will contain only some, some will contain many of one but few of another, etc...
I suppose you could sum up all the words that matched and get some form of score, but you can see how the complexity, number of combinations, and weighting of each field (Title, description, tags) can make things very difficult to pinpoint.
Additionally, executing such a query (or queries) to search and sort such a result set would be very hard to optimize and very expensive to run.
And add to that the ability to do fuzzy/partial matches of words, and phrases, and...
Well you suddenly start to appreciate how well google works.
