Final answer:
Cadenzas were written out in the Romantic era to express the composer's emotional intent and to meet the demands of improved instruments and broader audiences.
Step-by-step explanation:
At the end of the classical period and during the romantic period that followed, cadenzas were written out because the music style emphasized personal expression and virtuosity. During the Classical era, which valued clarity and form, cadenzas were often improvised by the performing artist to display their technical skill and creativity. However, as we moved into the Romantic era, composers wanted to incorporate their own emotional expression and complex virtuosic displays into the music. Hence, they began to write out specific cadenzas that were aligned with their expressive goals for the piece, thus allowing the performers to execute the music with the same level of emotional depth as intended by the composer. This was also a result of the shift from primarily aristocratic audiences to larger, more diverse public audiences and improved musical instruments, which demanded more elaborate and reliable performances.