Regattas hark back to the original traditions of sailing as a sport as opposed to a business, the object being to pit your sailing skills against the best sailors no matter from where they come. In the early days of "social" sailing/racing regattas were the "norm" and "club sailing" was almost non existant. This "tradition" still applies today, and if clubs/classes neglected to have regular regattas, then a very important part of sailing, as we know it today, would be lost, and we would be the poorer for it, besides, here in Australia, clubs run regular regattas, not just for the benefit to the sailors, but to put more "bums on seasts" at the bar and dining rooms before, during, and after the actual races(s) and to show a very healthy profit from them (the regattas) at the end of their financial year.
One very succesful regatta was conducted in England a long time ago, and you Americans were so impressed with the concept that one boat SAILED all the way there to compete, - that boat was called "America", so I would have thought that the first people to understand the "relevence" of "regattas" would be you "septic tanks"??