Why these leads behave differently
A lead form ad asks for almost nothing. The form appears inside the app, the fields are pre filled from the profile, and submission takes two taps. That is the whole design, and it explains both the appeal and the problem. You get volume at low cost, and the person who submitted did so with far less deliberation than someone who searched for your product, visited your site and typed their details.
This is not a criticism of the channel. It is a description of what you are buying, and it dictates the response. Treat these as warm interest requiring quick, friendly qualification rather than as requests for a quotation.