Why did Symphony No. 9 in C Major not receive its premiere during Franz Schubert’s lifetime?

Franz Schubert’s Symphony No. 9 in C Major did not premiere during his lifetime because the orchestra at Vienna’s Gesellschaft der Musikfreunde (Society of Friends of Music) found the work too long and technically complex to perform.1

Although the society had initially agreed to host the premiere in 1828, they ultimately refused to play the piece. In its place, Schubert offered his Symphony No. 6 (Little C Major), but he passed away in November 1828, nearly a month before that work’s public debut. The Symphony No. 9 remained unperformed until 1839, when Robert Schumann discovered the score and arranged for Felix Mendelssohn to conduct it in Leipzig.1