Why do later generations have diametrically opposite opinions on Zhang and Yan Song?

Zhang is a good prime minister. Who's Yan Song? He is a treacherous court official who has brought disaster to the country and people! His father and son were in cahoots, which made the Ming Dynasty a mess and made the people miserable. Such people are actually similar to those in Qin Gui. It's just that he hasn't completely brought down the Ming Dynasty, so there is no white iron to vote for Yan Song innocently.

Zhang, a man who helped the emperor when he was a child, managed Daming Mountain in an orderly way and the people lived and worked in peace and contentment for more than 40 years. But it's really a pity after death. The emperor copied the house and the 80-year-old mother was killed. In fact, the emperor is a bad king, and he is not a bad king. He has just been occupied for too long, so he has always held a grudge against Zhang.

But what kind of person is Yan Song? He is just a person who can only write green words and kiss up to others. In the imperial court, anyone who does not take refuge in his side will be impeached, either demoted or beheaded. Especially his illegitimate child, with a broken leg, is disabled. But if it is broken, it is almost bottomless. If you don't do good things, you will do bad things, and finally you will be killed behind your back.