The XML-like syntax is just less work, mentally and physically: no need for commas between props, the props object and children, no need to carefully manage all those commas when editing, adding, deleting, moving and removing stuff later on, plus the closing tag syntax makes nesting nicer by providing context via the tag name; all of which adds up to make it more pleasant to work with.
The second approach is what I was doing in various flavours for years prior to JSX. I ended up having to adopt comma-first to stay sane in larger/deeper templates, ( e.g. https://gist.github.com/insin/8e72bed793772d82ca8d ). The first thing I did when I saw JSX was start to write a React.DOM emitting version of my then-usual JSON-ML type stuff, but then I tried it and... never going back.
The second approach is what I was doing in various flavours for years prior to JSX. I ended up having to adopt comma-first to stay sane in larger/deeper templates, ( e.g. https://gist.github.com/insin/8e72bed793772d82ca8d ). The first thing I did when I saw JSX was start to write a React.DOM emitting version of my then-usual JSON-ML type stuff, but then I tried it and... never going back.