The reason is that you confined the quilt inside the pillow case. If you wash it again with say 5 or 6 color catchers, but don't confine the quilt, just put on delicate, it will give the dye laden water space to escape from the quilt.
Next time make a large plain fabric case if you think you need to confine the quilt.
For 13 years I dyed fabric for my rag rug business and bought plenty of color catchers. I was amazed at what they were able to do. I got out everything except some stain from dog vomit that was sick on some special medication.
Marcia