Like a funnel-shaped Colander?

A lot of leads never drop out the bottom of the sales funnel.

So, why do we call it a sales funnel?

David Daniels suggests here that "the lead qualification process" is more "like a series of rooms connected by doors" than a funnel.

I like his thinking.

His imagery (and image, go to link above) made me think that sales is really about having leads stay in the funnel-shaped colander until they drop out of the bottom, rather than fall out of a smaller and higher hole (or earlier hole).

Maybe like this Double Colander - Bon Appetit!