My two thoughts are, they aren't getting quite enough light, or they aren't getting quite enough humidity. My problem is, I don't really know how to get the 6-foot-long sanguinea vine into higher humidity or lighting. Humidity I don't think I can do, lighting I could maybe coil it and put a light over it? It's leaning against a South-facing window with a little bit of tree shading.
Or are they just not going to pitcher while they're vining? I would have thought they'd put out upper pitchers at some point.
How do other people keep large Nepenthes happy indoors? They're growing well enough and don't seem unhealthy, but I'd kinda like some nice big pitchers.