My friends in theater will probably think this is a silly question, since to us it makes great sense to do the G&S shows. But occasionally, when I tell people about my hobby, they seem kind of quizzical. "Gilbert & Sullivan? Sounds vaguely familiar, maybe. Operetta? Uhhh, that Brunhilde stuff?"
How did I get into it? In 1989 I wandered into the set shop of a show whose name I couldn't even pronounce: Iolanthe. I found people there doing fun things: building stuff, painting it, eating junk food. Eventually (after a lot of hard work) we moved all this paraphernalia (including the junk food) into the theater and, amazingly, people paid to come see it! Apparently they also paid to see people stand in front of it and sing, but so it goes.
Now, I've also sung in choruses off and on all my life, and I soon discovered that Sullivan's music was beautiful. I love multi-part choral harmonies and most G&S shows have a capella singing, too. One night I showed up at auditions just to hang out, and was surprised to find myself auditioning. My audition song was "Happy Birthday to You," since I didn't have anything real prepared. But I got in the show.
I soon discovered that my skills and passions were well suited for theater in several areas (that you can see from the pictures on this site). I also found that I loved having something substantial that I contributed to outside of work. A show requires dozens and dozens of people to produce, and then it's seem by hundreds or even thousands of people. I got to do artwork and actually have an audience for it (this is hard for artists to acquire). Or I got to sing. Or hang out back stage dressed all in black, which felt cool.
As for G&S, I do have a real fondness for the shows. They have a real charm. I've seen a number of other operettas of the era, and some are wonderful but some have left me appreciating Gilbert's sensibilities. Maybe this will explain it:
(They badger choruses to articulate because the audience will understand better. "Parsonified"?) This kind of language will help you understand why, if you do a few shows, you find yourself saying things like "Success has crowned my efforts!" (from Iolanthe), or "Modified rapture" (from The Mikado), or "Oh joy, oh bliss" (from who knows?).
In fact, G&S is so delightful that there are groups all over the world dedicated to performing it. If you want to see a good show, I recommend starting with The Pirates of Penzance. You'll probably be surprised to find that you recognize some of the music in it.