Twitter had been around for a long time and could very well be considered feature complete and run with a skeleton crew.
They don't own any mission critical software and in the days it went down after Elon started pulling the plugs, the only thing that changed was the people going to reddit to complain about stability.
Twitter was also effectively wrecked in a variety of ways and nothing really came in to replace it. Which may well have been OK. But it was the reality.
