There can be multiple reasons for the same. Two main factors are as below:
1. Targeting: You might be reaching out to a generic audience. Facebook offers plethora of options to precisely target your user segments. Its no more the generic targeting based on location, age and gender; there are tons of such parameters available now.
2. Communication: For an ad to perform; communication is the key. Despite of precise targeting your adverts campaign can miserably fail, if you don’t know the targeting well.

There are so many reason when we never receive any lead and query from fb ads
1 targeting
2. age
3. Banner
4. bid amount
5. low audience targeting

watch details video on this How to make FB ADS

Not delivering” means that your target audience is not seeing your active ads. This may occur with brand-new advertisements or with older, successful advertisements. Check the Delivery column in Ads Manager to determine if this applies to your campaigns, ad sets, or ads. Your Facebook ads may not be converting because you are using the incorrect ad for the stage of the customer journey at which you are targeting potential future customers. For consumers who are much further along the marketing funnel, the ad copy is more appropriate.

The reason behind a lack of conversion could be because your landing page doesn’t match your ad. In other words, people have a different experience when they reach your landing page because what is on the landing page looks too different from the FB ad, making them leave the landing page.