Jerry 47 put it quite well, they're good business people. They have a 'loss leader' sale item that brings people in the door and then the person buys several 'add-on' items which have a higher mark up/profit margin.
Ie: In the auto parts business we put a brand name of oil on sale. A person comes in wanting five quarts of brand-x oil. We don't make any money off of the oil, but we make a ton of profit off of the regular priced oil filter, air filter, PCV valve, cabin air filter, shop towels, hand cleaner, filter wrench, and the bottle of soda and Slim Jim (tm) that he buys at the same time.
Hence, when HL puts the kits on 50% off sale, they are anticipating that you will buy the regularly priced glue, knife blades, paint, inkjet printer decal making system, etc.
This is just good business.
To answer another poster's question, the reason that Hobby Lobby hasn't moved into the SF-O area is because of the nature of their business ethic. This is a company that's VERY steeply based in bible-belt type business ethics. To the point that the entire company shuts down completely one day per week, they are _NOT_ open on Sundays. Frustrating to some cus- tomers, but a lifesaver for many employees. It's nice for those people in the low paying service industry/retail sector to have one guaranteed day off per week. The 'fast food' establishment Chik-Filet is the same way, it's sur- prising to me that there are so many of them in shopping malls in the US, I know that many malls will fine businesses for not being open when everyone else is (my mom's retail store once was fined $1000 for having their gate down five minutes too early!).
Anyway, up here in the frozen north of Fargo, ND we FINALLY got one just about a year ago. They've had the coupon special twice and the regu- lar 50% off sale at least twice. I've snap[ped up some decent a/c kits each time. Picked up a Testor's B-2 kit for about $13 the last time!
Hope this helps!