score:11
Olympic Games in old Greece were traditionally held every 4 years. Modern olympic Games respect that tradition. While in the beginning of modern Olympics, there were little economic pressure on the host (there were not as many sports as present day and no expensive infrastructure was needed), nowadays, it is just not economically feasible to hold them more often than once in every 4 years. (Bear in mind that Winter Olympic Games are also held every 4 years, but on 2 year delayed cycle)
Regarding other big competitions like FIFA WC and others, they face the same problems. Stadiums are expensive and every country organizing such a competition must build them. Please note that the host is known much earlier and the city/country has much more time to prepare - typically 2 or 3 cycles which is 8 to 12 years.
So that's the first reason.
Also, it could be a problem if other major competitions overlap. If, for instance, Olympic Games are held every 4 years and FIFA WC every 3 years, then every 12 years both competitions would be held at the same time.
That would be a great problem because the athletes would not be available for both competitions, TV could not follow both etc.
So the second reason is also of practical nature.
Upvote:3
First, not all world championships is every fourth year: Ice hockey is every year, athletics every second. However, I could not find any event held every third or every fifth year, so this does not really break the basic four-year pattern (Badminton seems to have used a three-year schedule for a while, but is now on a four-year one). This supports the theory of a general connection with the olympic schedule.
In many cases, also, it seems like the olympic games were for many sports considered as the world championships. This is the case of e.g. football ("soccer", if you're from the US), athletics and ice hockey. While this obviously, did not guarantee that it would continue to be held every fourth year, it did establish a basic pattern.
Also, one should consider that one can probably not have events more dispersed than four years: for most sports, a four-year schedule means there will only be two or three world championships during the best years of a career. A five-year schedule would reduce this further. Together with the wish to avoid two large events the same year, this would mean cycles of two or four years. For some sports, it appears that reducing the value of every fourth world championship is a bearable cost, so theycan have events every year.