Because Tailwind is often suggested as a way for novices to implement design without having to really learn CSS. Simultaneously, allows people who don't care at all for CSS or design to create something functional.
Tailwind does not require knowing CSS. It'll get you around tailwind faster if you do know it, but you do not have to care about what Tailwind is really up to when adding "outline outline-2 p-4 outline-offset-2". This is a major reason why people pick it up in the first place, to ignore CSS as much as possible.
They can't explain the difference between an outline and a border though, and especially can't explain when to use which. If you try to use Tailwind without understanding that, you're gonna have a Bad Time™.
But almost every Tailwind shortcut translates to one line of CSS. So you need to know CSS, for example you understand words 'padding' and 'margin'. I did not know these words mean before learning CSS.
Tailwind does not require knowing CSS. It'll get you around tailwind faster if you do know it, but you do not have to care about what Tailwind is really up to when adding "outline outline-2 p-4 outline-offset-2". This is a major reason why people pick it up in the first place, to ignore CSS as much as possible.