m6.12xl are 48 vCPU systems. 25 million cores is a hilariously huge amount of compute to use to run a site of twitter size, which I guess does point to how much tech debt they have ignored over time.
Twitter is the 4th most visited site in the world.
But they do serve videos, which possibly they have to transcode or otherwise process on import (?) They probably also have some filters for pictures to remove porn and stuff like that.
This can amount to serious CPU if you have millions of users uploading that stuff daily.
A pure text-based Twitter would be much smaller.