Why is there so much campaign-like activity after the polls have been closed?

Question

2020 US Presidential elections polls have closed, but there is still high activity coming from candidates almost as if they are still campaigning (e.g. 1, 2).

From a layman living outside the US, this is rather strange. Having a statement immediately after the polls are closed makes sense, but so much activity between polls being closed and the final results being announced seems useless.

It is interesting to see those numbers being changed and counties and states becoming blue or red, but whatever candidates are doing (political statements, tweets, press conferences) cannot influence the voting since it has ended. It is a matter of time until the counting is over.

Question: Why is there so much campaign-like activity after the polls have been closed?

Answer 1

"Indeed, you won the elections, but I won the count."

— Anastasio Somoza Debayle, President/Dictator of Nicaragua

The polling stations in the US might have closed, but the race for the presidency is far from over. The incumbent has repeatedly questioned the legitimacy of mail-in votes (which are assumed to be far more popular with the supporters of the challenger) and argued that they should not be counted. There were also other accusations from both sides that the other would use various methods of election manipulation which, if proven true, could lead to the invalidation of votes.

That means that this election will very likely not be decided in the voting booths but in the legal courts. While public opinion and legal arguments made outside of the courtroom should not matter in a court of law, it might still influence the positions of the judges. Also, all these legal proceedings aren't free. The candidates will have to pay for them out of their now depleted campaign funds. So it's not unlikely that both candidates will have to do more funding runs to fund their legal challenges to the election. Which has already started (Business Insider: Trump still begging for money as votes get counted).

Which is why it is important for both candidates to not be perceived by their supporters as not even trying to put up a fight against the alleged misconducts of the other candidate. Being silent might be perceived by the public as legitimizing the behavior and statements of their opponent. When Trump claims he won the election before several key states reported their results, then Biden can not just leave that uncommented, as that might be perceived as a concession. When Biden claims that counting the mail-in votes will turn the results in various states in his favor, then Trump can not leave that uncommented, as that might be perceived as him backpedaling on his stance on the legitimacy of mail-in votes.