Could be your overall narrative is not that compelling OR
Your pricing or terms are too high with no flexibility perceived OR
You are not hitting enough people to build a pipeline OR
You are hitting the wrong target market.

Having said that, you have to gauge urgency in the first call. Depending on your market, you can gauge directly or indirectly.

Direct: You ask them for their timeline to start.
Indirect: Ask them if they have the budget and be super straight.

In either case, the first few points above must be handled - otherwise, they will never buy in the first place.