That's some strange logic you use there. Let's apply it elsewhere. Evidently congress did not consider Whitewater, Chinagate, Cattlegate, Vince Fostergate, Travelgate and all the other non-Lewinsky scandals of Clinton bad enough to warrant impeachment on their basis so I guess none of them were bad either. And Congress didn't consider Teapot Dome bad enough to impeach Harding or any major figures under him or Credit Mobilier bad enough to impeach Grant or any major figures under him, so I guess none of them were anything bad either! And Watergate? Well, Congress never quite made it to impeaching Nixon either...must not have been anything bad. Funny how all these scandals work out for the better when the only means of expressing disapproval is limited to impeachment...which must also mean that there have only been two major scandals in American presidential history!
And maybe those events, while bad and scandalous did not reach the level of Impeachement.
However, Clinton did get impeached for lying under oath.
Lincoln did not.
I am sorry that you do not like the way checks and balances work in our country, but if Lincoln were the tyrant that you think he was, impeachment would have been the responsibility of the Congress, just as it was when Clinton was impeached.
As for Nixon, he was forced out to avoid impeachement.