When the order schedule is enabled, why is the order quantity for today larger than the order quantity at the next scheduled reorder date?

This is basically because the system is suggesting enough stock to also cover the time between now and the next scheduled reorder date. So the total period of cover is from now until the following reorder date, which is a larger time period.

This isn't always the case, but sometimes if your next scheduled reorder date falls within the current lead time or order frequency, this situation can occur.