CSS modules is a (great) mechanism for providing isolation, very useful in the context of today's component-oriented front end development.
Tailwind provides some (quite good) building blocks for a design system, such as a palette, a sizing scale, values for shadows and rounded corners... and a vast set of classes to apply them. The set of classes covers basically every CSS feature, making it possible to slap everything in the class attribute of your HTML elements and never or almost never have to deal with CSS files.
In other words, CSS modules is a solution for those who love CSS and needed just a way to not deal with naming clashes without resorting to BEM. Tailwind is a tool for those who very much would like to avoid writing CSS
i like to use it with DaisyUI also. the part i like is that all the classes i need are already written so its just putting pieces together.