I bet 20% of their workforce was support + inside sales reps for advertisers.

I'd further guess that 10-20% of their workforce was staying on top of regulations. If twitter works, but does not comply with the FTC consent order and gets fined out of business, that is not a technical failure but still is failure.

Large enterprises, especially those under consent orders, spend a TON of effort in compliance. Given that environment is constantly changing, there is net new work needed in almost a Red Queen effect.