It also keeps with the ideas shown in the various seasons like how Angemons' body turned to glowing dust particals as he died, leaving behind his bag. Or how they were absorbed in tamers. Heck even Savers/Data squad with, the Gizumons erasing a digis data entirely. We've yet to see one actualyl bleed- to my knowledge-but we've seen what it looks like in most seasons when they die, so having that sort of stuff leaking out from them makes sense. Plus we have movies that reference blood, like bloody mist (myotismon's attack) So I'd assume they have something that acts similar to blood. It may not look like blood, they are made of data so why not loo like data- be it 1s and 0s or colorful squares(dgigisoul) or even just specks of light(Adventure and Tamers i think)