The times of the events before the Tribulation, like:
The Great Apostasy
The One World Government
The Great Lie
The Rise of Mystery Babylon
Are called "the last days" and "the Endtimes" in the epistles in the New Testament. The Endtimes does not automatically = the Tribulation. The Tribulation and more specifically the "Great Tribulation" is referred to by name.
Mostly because there is persecution before the Tribulation. However, it is not as severe as the Great Tribulation, so the Persecution before the Great Tribulation is called "the Endtimes" because it is close to the Last Week (Great Tribulation) in Daniel. 2 Esdras would have called it something other than the "last days" if it was the Tribulation, Endtimes are the last part of the Church Age.
That's why Pre-Tribs (me included) sometimes say things like, "Are we living in the Endtimes now?". Since Pre-Tribs believe that the Rapture is before the Tribulation, we would not call an era of persecution "the Endtimes" if it was the Tribulation, since we believe that the Tribulation does not happen until the Man of Sin (Antichrist) appears after the Restrainer (Holy Spirit and/or Church) is removed from the world.