The advantage is in both the speed of the shorthand when transferring the CSS you know you need for a layout from your brain to the element (flex items-center gap-2 vs. display: flex; align-items: center; gap: .5rem; - just try typing them both out), plus all the stuff inline styles can't do, such as variants based on screen size, colour scheme, user preference, pseudo-classes, parent/sibling state, etc. which you can get done in one place in one file in one sitting.

The money wasn't coming from that.