You can still use your own custom classes with Tailwind.

And then you've come full circle though right?

I wish I liked tailwind it's all the rage but I just don't

You can still use normal css if you're styling multiple things. I think tailwind shines mostly when the css does not need to be reusable or is encapsulated in a component which is how it works in some modern web frameworks.

The reason why it is big is efficiency. Once people know those class names by heart, they get a "nice" (arguably) default style very quickly without jumping between multiple files. This matters more than one might think..