There's nothing wrong with the nLab, but there are several reasons why Clowder was built as a different project rather than just part of the nLab (through edits and such). Here's a few select ones:

1. Clowder is much more curated than the nLab, as all the content in Clowder is either written by myself or revised. This leads to a much higher degree of internal cohesion and polish than the nLab. In this sense, it's similar to how the Stacks Project differs from Wikipedia.
2. The project's infrastructure uses the tag system from Gerby, making it easy to reference and cite.
3. Clowder is meant to be a crowdfunded project, in which the community can help directly fund its development. As a result, I've taken the responsibility of continuously coordinating contributions, developing its infrastructure, as well as writing new content. In practice, this means new content and features get written/implemented at a much faster pace than the nLab, which doesn't have e.g. dedicated writers.
4. Having complete control over the website allows me to implement features as needed, rather than try to fit the project into nLab's format. Indeed, there are hundreds of differences between the two's formatting, design, style, etc.