Plants in general get floppy if they are too dry, so lack of water is a possibility. Or it could be the type of tulips you have is floppier that those you are seeing elsewhere? I've notices that my Apricot Impressions, for example, have leaves twice as wide as most other tulips and do sprawl a bit. Also some of my tulips have ruffled/wavy leaves while others are straight. And the species tulips tend to lay in a star shape on the ground, they don't really have much in the way of stems.