I'd imagine that infrastructure costs are rather significant for Tailwind, and that there are non-neglibible organizational costs as well.
Even if Tailwind were a shared hosted system like the common bootstrap CDNs of old… CDNs are dirt cheap for a small text file, even if it were loaded billions of times a month.
Some back of the napkin math suggests that it would cost about $300 per billion downloads for the current bootstrap.min.css file (gzip compressed, naturally) at North American network prices on one CDN I’ve used before. Or just $150 per billion globally if you're willing to use fewer PoPs. With browser caching, even split per domain, a billion downloads covers a very large number of users for a very large number of page loads.
> Vercel sponsors all of our hosting for all of our sites (which is expensive with our traffic!) for free and has for years