Perhaps they are guarding the location?
I had a bait hive last year that had a good bit of interest over a few days then fighting at the entrance with obvious guard bees similar to a normal hive. I think one lot of scout bees were defending the hive over another lot. This hive had nothing inside that could be robbed.
The swarm finally arrived on the sixth day.
That's interesting - I've just seen the exact same thing with my 'bottom of the garden' bait box.
The weather has been unbelievably wet - but during the last dry spell I had a dozen or so looking interested, then that number increased to at least 50, plenty of measuring-up and so forth, and then the heavens really opened-up and a dozen got trapped here and were forced to 'bed-and-breakfast' for a few days until the storm passed - so I gave 'em a spoonful of 1:1, as they were looking very miserable and dejected.
Today the sun finally came out, and a good 150 or so were buzzing around the bait box - 'frantic' is the only word to describe their behaviour - several of them got involved in wrestling matches on the landing board, others seemed to be trying to mate with other workers. Mass confusion reigned (at least, in my mind). And then they all left.
I figured it might either be aspirational robbers attracted by the lemon grass oil and propolis, or maybe two lots of scouts in a real estate contest. Just in case it's the latter, I've put another bait box out, about 15 feet away.
Just have to wait and see.
LJ