He lost (by a lot) in November 2020 because his supporters didn't number enough to re-elect him.
The people who rejected him in 2020 aren't going to change their minds about him - so where are the votes he'd need to win in 2024 going to come from?
The GOP isn't working on "getting out the votes" - instead they are telling their constituents that elections are rigged, which will surpress turnout among their own voters who believe their votes won't count.
The MAGA movement is diminishing, not growing. So again, how does Trump get enough votes in 2024 when he didn't have enough votes in 2020 when the MAGA movement was at its peak?
Many Republicans have left the GOP as a result of Trump's antics. They aren't going to vote for the guy that they abandoned their own party over.
Trump lost last November - which was before the events of January 6th. Many were horrified by what happened, and won't be voting to re-elect the man responsible for it.
Last November's election was also before the revelations about how he attempted to overturn states' elections, and bully them into not certifying their state's vote count. "Just find me 11,800 votes." "Just say the election was corrupt, and leave the rest to me."
The 2020 election was also before the indictment of the Trump organization, and the ongoing investigations into Trump's illegal activities both while in office and in his personal dealings.
Not all Republican voters are Trump-humpers, and many of them would sit out a 2024 election if he's on the ticket after what they're learning about him now, and what they will be learning over the next three years.
So that begs the question: If Trump didn't have the votes necessary to win in 2020, how is he going to get the votes necessary to win in 2024? Where are they supposed to come from?