There isn't much payoff in that for politicians. The people who will respond positively are already on board. Rather than win over the undecideds, politicians who point out press bias get cut up by the media for complaining. They look after their own. Look at what happened to Nixon. Since then, politicians try not to focus on press bias but try to work around it.
The old adage about "never pick a fight with anyone who buys ink by the barrel."