Why do Incumbency not Benefit Politicians?

-Presidents take the Blame: Either for their own Policies or just Events in general. Biden may suffer due to Economic Hardship. Trump and his Wall -Incumbents don't always raise More than Challengers. Money doesn't = Success. The Incumbent Party in 2016 lost even though they spent Considerably More -Challengers gain Publicity too. Trump has basically a Magnetic Field of Media Attention