Why does jury trial day keep being reset?

There is not enough information to answer. There are a million reasons that a jury trial can be reset: another trial is ongoing, the room is unavailable, one of the attorneys has a conflict, a critical witness has a conflict, the judge has a conflict, either side wants more time to prepare, there is forensic testing that has not yet been completed, new evidence has surfaced and needs to be investigated, and those are only a few. Your trial could have been reset for one of those reasons, or another reason entirely. You should speak with the attorney on the case. The attorney can often give you a clear answer. Sometimes the reason is recorded in the court order changing the date. If so, you can contact the clerk of courts for your county to check on it. Most courts would not schedule more than a single jury trial in a day. Many trials, however, end up taking longer than predicted and spill over into other days. Hope that increases your understanding of the process a bit. Good luck to you or your loved one.

Mr. Canon spelled it out precisely. These could be a hundred reasons. Need more info.