How does a 75% workforce cut even work logistically for a company not on its deathbed?
Sometimes a 75% workforce cut is exactly what a company on its deathbed needs. In the case of Twitter they wouldn't even need to fire anyone. Just make employees sign a statement reaffirming their commitment to free speech and the 1st Amendment (ala forced DEI statements at other companies) and 75% of Twitter employees would likely depart on their own.
Most Twitter employees (like people everywhere) go there to earn a living and as long as employment conditions remain acceptable they'll sign whatever management ask them to.
In particular if it's a meaningless broad statement such as "commitment to free speech and 1st amendment".
Most people there don't have anything to do with policy enactment or enforcement so why would they care (case in point those other companies, you mentioned which also retained their workforces).
If the real consequence is a work culture in which bullying and harassment is sanctioned (or even encouraged) by management THEN people will leave because it's unpleasant to work in such an environment.
The ones remaining won't necessarily be your high performers