I also wonder why it didn't surface during the primaries, if the rumor that it came from the GOPe are to be believed (unless they didn't have it then).
The tape was in fact being held for the last week. It was released early in order to blunt the damaging wiki leaks release on Saturday. They didn’t want to release it, but had to and it is working. Look what every news channel focused on since Saturday - the trump tape and not those devastating Hillary emails.