Is it because of this reason? thanks
less likely the case,
your website authority is too low, your content isn't that good, or/and your website is flagged by Google, etc...
internal links, silo and other on-page factors can play a role, but the case overall, it's a bad signal for your SEO,
wordpress meta titles are usually added by wordpress,
meta descriptions aren't really required, so normally pages/posts should show up in the SERPs,
ofc, there might be some technical issues causing the problem,
but since the articles are indexed as you pointed out, this is just an SEO problem,
you should try to improve the website overall,
make sure you're using the right content, matching the user intent, unique & good quality,
add internal to the posts, contextuals, menus, sidebars, etc...
and lastly build some off page authority,
also, if the website is just brand new, you should give it some time,
pages won't rank overnight and you might have such problems in the intial period