We do a lot of things in league manager that are not in game so I don't see how the trades not being available in game is relevant. It's not wise to a.ssume people know something that has never been stated.
The stuff leagueManager does is superficial. It just adds stuff on top of things. It doesn't actually change code the code. Cap, trades, etc., it's not adding anything to the actual game itself. If you can't do something physically in the game, you can't do it on leagueManager. There are other sites that do this too.
I take back my a.ssumption. I actually didn't think about anyone making trades in the offseason at all, because I said before, you can't do it in online franchise. Didn't cross my mind that people would try to trade in the offseason and leagueManager would allow it.