Because you can ship in a few days instead of wasting weeks trying to bike shed through something as basic as css.
Use tailwind as a tool, have a component library that can be put together in a couple days max, and now you have ubiquitous styling language and don’t need to waste hours on css of all things.
Then on top of this we have components library with common basic components and layouts
Then inside the apps we use the components and that Tailwind config and it works quite nice.
We have rules for tokenized colors and sizes so it all references the config.
There are problems and all, but all in all I think is quite good