I think their business model was sustainable, but depended on SEO. AI made it so people would either use the LLM generated tailwind syntax, or the "AI Overview" at the top of the Google search results and never land on the official tailwind documentation site. Less visits on the official docs meant less people would see the paid offerings, which means less people would buy.

It's possible they could have explored other marketing channels (youtube?), but it seems like the death of SEO for this sort of content lead to the main issues.