It's not necessary for world leaders (with all their entourage) to attend every year, and the total numbers should come down, it's a big waste of energy, especially regarding aviation emissions.
Only a handful of people in a few small rooms can actually change anything in the key decision texts - the other diplomats repeat old positions, and most other participants are just there to lobby for support for their projects.
I recall the early COPs - attended COP2 with only 2000 people, not 80k like last year. Also COP15 where world leaders did turn up, but didn't conclude.
The discussions leading to big decisions are are a multi-year process. COP30 next year in Belem, where new targets are expected, is more important than this year (fortunately, given weak choice of host government).