Although it is perfectly possible to give each day's short position total, FINRA chooses to compute this information only twice a month. Therefore, shorts can plan their sales to be closed and re-entered in ways that will not disclose their true short position. If this data were reported every day, this would not be possible. And there might be quite a bit less trading by shorts.

Gee, I wonder why FINRA doesn't report the data every day?