1. If the Constitution doesn’t require the states to all appoint their presidential electors on the same day, then why do the states all appoint their presidential electors on the same day?
2. If the Constitution doesn’t require the states to all appoint their presidential electors on the same day, then why did the Trump electors in the states where the Trump campaign was trying to challenge the election results convene on that same day to formally announce that they were casting their electoral votes for Trump?
Because all states have chosen to allow the electors to be appointed, so to speak, by the voters and the day for the election is uniform throughout the country. If a state decided to have the electors appointed by the legislature, as South Carolina did up until 1860 for example, then the legislature could appoint the electors on any date they decided so long as the electors were chosen in time to cast their voted on the date specified for doing so.