What made the residents of Maycomb so attracted to watching the Tom Robinson case in To Kill a Mockingbird?
Several good points being made in this discussion. The most accurate might in fact be that observing trials was a cultural issue--one that continues today. Back then they had the real thing, but today there are channels like Courttv. Let's not dismiss the fact, however, that many people had a purient interest and were merely there for the salacious details. Many were there to make sure that Tom Robinson got what the likes of him deserved. Very few were there to see justice carried out.
Not only is the trial one that threatens the status quo, but it is one that also promises entertainment as the degenerate Bob Ewell is sure to "say anything." There is often a curiosity about the lower element of society, and, besides this, in a small, sultry Southern town, anything that happens at the courthouse is big news and a curiosity since most members of the town know all the other residents.
This cultural practice of going to municipal events is evinced in the Friday night football games of modern times where the residents not only support the local team, but they assemble to see who else is there. For the small town of Maycomb, a trial also provides entertainment and gossip.
To expand on the point about race, I would argue that most of the white people are there because they want to be reassured. As far as they know, a black man has raped a white woman, which totally upsets the way society is supposed to be in that time and place. They want to be reassured that things will go the way they should and that Tom will be convicted and punished harshly. So there is this real need on the part of the white population to go watch so they can feel that society still works the way it is supposed to.