I don't know. It ain't all THAT early. I've seen most of mine locked up at least once now. I was seeing some lock up a couple of months ago. Either they'll go or they won't. A few things to help it along would be to introduce two males together and let them wrestle it out. Pairing up when a low pressure front moves through works wonders too. You can also try misting a bit to increase humidity, I've been told that humid air carries the females scent better. Also introducing your male after the female has shed (leave the shed skin in the tub) adds more aroma to the atmosphere. Popping some sperm plugs out of another male and rubbing them on the back of the female you want to get bred has also worked for me in the past.

Also, how do you know they aren't doing it but are just shy? I've got a male het albino that I've only ever caught breeding once. Yet he's produced 2-4 nice clutches for me every year for the past 5 years (though I have noticed that his females tend to be more grouchy then my other girls, maybe they're just not being satisfied.... ) .