Yes it is taught in school. But have you ever thought to think why? Is it because he is the greatest writer that ever lived? Or is it because he was in favour with the British monarchy who use tradition as a way of maintaining power and the status quo and who then went on to conquer most of the planet, exporting their culture as they went? The upper class Oxford and Cambridge professors who determined the curriculum would have made studying his works mandatory and other universities would emulate. A couple of centuries of inertia and you end up where we are today.

Notice you said Shakespeare is taught in high school. In that sense it carries importance in that people are exposed to it whether they like it or not. But it doesn’t mean that once those people leave school it continues to be of importance to them and to most people I would argue it doesn’t. The majority of people run a mile when you start mentioning Shakespeare because they have less than fond memories of being sat and forced to read something written in archaic English that in the present day requires either a teacher or another book written in modern English to understand if you have never encountered it before.

The original comment talked about “most important novel of the century” which is a ludicrous claim. The assumption in that sentence is that there is a universally agreed upon consensus for evaluating literature in comparison with other literature that allows us to rank them like you would football teams in a table and that the commentator’s choice is the undisputed winner of this gladiatorial death match. If you can point me towards this criteria please do so. Otherwise what you actually have is ‘This is the most important thing to me so I’m going to assert grand unprovable statements as proof in order to propagate my personal tastes and beliefs”.