Nothing, but a lot of the web dev community feels like we've gone overboard in terms of bloated CSS frameworks and this is what I perceive to be a reversion back to the basic ability to style a document without much need for writing and learning CSS or the frameworks themselves.

As a full-stack dev who has started/but not finished tons of side projects because I hate the design part (okay, I'm more backend than frontend, I like vue/js but css/scss isn't my favorite part of the stack though I can do it in bulma, material-ui, vuetify/etc....)

I think this sort of thing looks cool, though picnic.css (https://picnicss.com/tests) -- from another comment seems more my flavor.

Might be a good way to focus on the functionality, maybe use it w/ tailwinds for extra styles where needed, and launch faster make some $$ hire a person to do the design stuff I hate to do in an actual framework or something and launch a prettier v2.

Nothing's wrong, the supposed advantage of this is that it's less complex and the only thing you need to learn is html.

Which most people that would use this already know and so really you can just skip the learning and go straight to using it.