The magical bit is that they have hundreds and hundreds of cooks in the kitchen, who all need to justify their existence by creating tons and tons of little one

The magical bit is that they have hundreds and hundreds of cooks in the kitchen, who all need to justify their existence by creating tons and tons of little one-off UI screens for obscure features that hardly anyone sees or uses. This kind of team structure also causes other strange-looking technology choices, such as CSS-in-JS: they have to do stuff like that because they literally cannot prevent different members of the team from writing CSS class names that collide.