We've always had a bloody egg every now and then, but lately there's a couple every day - pretty bloody, too. Why does this happen? We have a rooster, the hens are all healthy, though they have been confined for several weeks to the coop and pen due to several feet of snow in and around the pen.
I'd suggest you check "blood spots" at this link. I think it can help you.
Egg Quality Handbook
I kind of suspect genetics and maybe a vitamin problem, but you are there looking at them and the conditions. All I can do si make a wild guess.