Top tier talent generally goes where they get compensated the best

Twitter does some cutting edge ai research, they are unique (just like meta and google and some other firms) in that the challenges they face at the scale they do are unique, and need unique solutions. If you think "social media algos" are a) not cutting edge or b)all Twitter does technically, then you are incredibly misinformed. It's not just Twitter, Google and Meta are also doing incredible research in AI and are among the biggest contributers at any platform you choose (conference papers, libraries, datasets, architectures)

What self-driving car are you talking about? I’d bet Twitter has had more success in computational neuroscience with their structured tweets than Tesla has had with broken roads.