The syntax highlighter has changed on all Stack Exchange sites: now it is only enabled if the question contains specific tags (mostly language or framework related). Since all questions on this site are about WordPress, we don't use the wordpress or php tags, and none of the new questions get syntax highlighting.
I think the WP SE should have the default syntax highlighter (without language hint) enabled, since it seemed to work pretty good for our needs (PHP, HTML, JS, CSS, occasionally SQL). Otherwise we would need to add almost every tag to the syntax highlighter.
I'm tagging this question bug in the hope that it gets noticed by one of the overlords...