Sometimes companies - I can think of 4 who regularly do this - post a lot of jobs for one client but do not need that many completed. They might post 50 locations when they actually need 25 or 30 shopped. When they get the number they need scheduled, they either remove the posting or leave it active just in case - some of those scheduled may not be successful or may be not performed, requiring them to schedule more.
There can be a lot of reasons: Rotation, number of shops assigned to one shopper, not wanting to assign to a shopper who applied, the possibility that it appears the client may cancel the shops, or simply because the scheduler is busy and has dropped the ball.
It's not bad to contact the scheduler and make an offer.