Why Google not showing the meta description ?

Google has not been showing the metadata description for a while now. I guess Google is trying to test it on selected domains or something like that.  The thing is that Google has too many factors for deciding the ranking of a page and meta description is only one factor. One reason for low ranking could be because of a poorly written meta description or a bad user experience.  I am not fully sure, but I am guessing that is the reason Google is doing this.  If you have any more info that is related to this, do let me know.

wait for the indexing.

My new and not well ranked blog reliably has all meta descriptions showing properly in Google. I would look over technical requirements like character length. Find a good article that contains all the rules. Make sure your meta is also completely related to the content. Also make sure you have quality content that doesn't produce bounces. If people are bouncing then Google might get signaled that your meta isn't telling people what is in the content. Also I thought I read there is no guarantee that your meta data will be displayed. I would start reading all the guides you can find.

If you've updated your meta description recently, you may have noticed that it no longer appears in the search results. This is a common problem, but there are several reasons why Google might show the old meta description instead of the new one. This happens when Google rewrites the meta description to better match the search query. In some cases, Google may also highlight certain text in the meta description. Here are a few ways to fix this problem.

A good meta description should tell Google something about the page. If it's not relevant to the page's content, it may substitute a sentence from your body copy. This happens most often when your meta description reads like an ad copy, and it's an indication that your meta description needs to be updated. To avoid this, make sure your meta description is descriptive of the page, and doesn't sound like ad copy.

If you're still seeing the wrong description in the SERPs, it's possible that Google is ignoring your meta description for a variety of reasons. Google has been secretive about its algorithm, and you might have to rewrite your meta description to make it relevant to the content on your page. However, if you're not seeing the meta description you're after, you can always use the data-nosnippet attribute to wrap the content that Google has decided is unrelated to the page.

If a better content is available on the page for a search query then Google will ignore showing the meta description value in the SERP. How you can avoid it is, make your meta description value more relevant to that search query. This is the only solution to it.