system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do members of an orchestra need to read music to perform a concert yet members of a band don't read music in concerts?

Does the length of the music make it difficult to remember the different nuances?  I can't imagine that they practice less than a band.  It seems more difficult as a band member because they would have to know many different songs.

*edit* Thank you all for your reply's. I've been teaching myself the guitar and wondered this while I was talking things over with my wife.  I had the feeling that the simplicity of rock songs versus a classical piece was the core issue here.  I appreciate all your input and time! :)
gpt
Orchestras can be anything from 30-100 strong. The pieces they play, instead of 3-5 minutes of pretty repetitive music (not to be rude on pop/rock/etc in any way, but there's a structure, and it's easy to learn) are usually around half an hour to an hour long, although this varies hugely. Orchestras are tricky to coordinate and it's a risk to ask that many musicians to memorise a huge piece.

On top of this, there are a lot of directions the conductor would have given the orchestra in the rehearsals that depend on performance practice as well - different time periods had different styles. All the sections have to play exactly the same, and this has to blend with all the other sections of the orchestra.

Band members have probably also written their own materials, and it comes more naturally to memorise this than an hour long symphony.

If it's an opera, you also have the singers to consider - they will have their own nuances that will most likely change each night and it's much easier to anticipate these if you have your music in front of you.