My reasoning is twofold:

1. Before Tailwind was introduced I could keep my style overrides in a stylesheet separate from my freemarker templates. When it came to upgrading my freemarker templates I could easily see FusionAuth's markup changes, diff those with my templates, and work through the migration without too much pain. Styles almost never came into the picture - they just worked across numerous upgrades. Unfortunately now my upgrade process includes a lot of noise since FusionAuth's Tailwind style changes are all mixed up in the markup. This makes it difficult to pick out the important changes to the markup and logic in freemarker.

2. Tailwind itself is ill-suited for pre-built themeable templates. I can't make changes to the Tailwind classes in FusionAuth templates because the CSS is already built (e.g. I can't reference a Tailwind class unless FusionAuth used it for the default template), so I'm forced to live in an in-between world with Tailwind and vanilla CSS overrides. Additionally the overrides become quite tricky because semantic class names have been removed (nothing to hook into) and Tailwind's generated styles are quite complex (e.g. border-top/right/bottom/left all being set independently for the same border).

My 2c. I'll keep struggling along and will be fine, but I do think Tailwind is a step backwards for FusionAuth themes.