As a matter of fact, I have heard a "classical" string quartet play ragtime. I've also heard a reed quartet play ragtime, too--& all by Eubie Blake. I have heard a "symphony" orchestra play The St. Louis Blues, too.   
I rather enjoy Big Band Music, as well as Dixieland, various tangoes, March Music by J. P. Sousa & other composers, & Music from the 1890's & lots of other Music. I have enjoyed concerts of Big Band Music which lasted longer, & the crowd--including myself--asked for more.
    If one is attending a concert of Music which one is uncomfortable with, I can certainly understand declining, or perhaps even stepping out for a bit. If I were being strong armed with having to be in attendance at a "rock" concert in this day & time, I would most likely suffer an accute 24 hour illness just prior to leaving for said concert. I can no longer physically tolerate the distortion of sound & the dangerous volume.
    If the band/orchestra was hired to perform Big Band Music because it is billed as being Big Band, then the Band certainly should honor the reason it was hired & perform Big Band Music.
    I play a wide variety of Music as do my band mates, but when my band is hired to play Irish Music, we play only Irish.