Two reasons:
Convenience. I'm going to be buying some anyway for the dragon, and Reptilinks requires a minimum $75 order to ship. $75 worth of links is a lot for one dragon... though Reptilinks also sells whole animals so I can combine orders if needed.
Cost. In my small little town, it's hard to come by food for any of my reptiles. I pretty much have to have everything shipped in. Reptilinks offers a variety of different links with rabbit, quail, rat, mouse, ASF, etc, and their shipping is reasonable. If I can offer my reptiles more variety at a cheaper cost, it's worth a try.