The decline started earlier
Twitter was always a company with an "eventually we'll come up with a business model" strategy. Good marketing to its main users – lazy journalists – saw it become popular for celebrities, subsequently followed by politicians craving publicity, but never with a convincing business case and caught between the Silicon Valley, or perhaps more specifically San Francisco, bubble and the real world. It had great user numbers but no good way of making money from them. Moderation kept the most active engaged and companies looking to advertise their brand, but came with high personnel costs. Then along came the SAFA, and I think I'm using the term correctly here, narcissist, who wanted to be king of the dump. He certainly cut costs, but removing moderation encouraged long-standing users to leave and many advertisers left, not to return because creating a positive brand image is difficult in a torrent of hate speech.
But the biggest problem was maintaining a value proposition in a changing market. From the start it was susceptible to bots and I'm proud to know my port of ifyoulikeitsomuchwhydontyoulivethere.com to a bot is still in existence, though inactive since it switched to OAuth! Evgeny Morozov amongst others highlighed the problems with echo chambers on social media, but Facebook then Instagram then TikTok and others found ways to swallow their conscience and earn lots of money anyway. But Twitter stayed pretty much as it was, remaining the darling of the chatterati but failing to attract the right kind of advertisers to pay for them. Even the laziest journalistst got the hint and started quoting from other services: Mastodon, Bluesky, Telegram, et al. It's going to be folded in Musk's AI business but this is now for PR purposes – I mean which self-respecting LLM wants to be based on content that has been largely machine produced for over a decade?