It’s intentional. Maybe not this specific case but Trump and friends being allowed to go on for so long is calculated.
Twitter has no real platform. It is fundamentally poor for information sharing. Their shareholders, thus the top-down decisions, revolve around number of users because number of users drives advertising metrics which drives valuation.
Keeping people on the platform cannot be achieved by actually using it. They rely on hype or outrage. It is the same reason they could eliminate bots overnight but have not done so. It would reveal that a huge percentage of their users aren’t actually users and the traffic would go dark.