We are trying to discourage daytrading of salary monsters, buying them to play one match and then selling or firing. We have already implemented the mandatory minimum four days to make sure you have to pay at least one player's salary. If this means that players with very high salary end up being unwanted, so be it.
With NT players, the situation is even worse. Firing them before having at least one training update would mean that they can be bought and fired over and over again without ever changing game shape (or receiving training). It just wouldn't be fair in the NT realm.
Having NT players is a tradeoff, they give you prestige and more merchandise but you can't fire them like normal players.