What kind of fertilizer did you use?

I don't remember off the top of my head. It's in my shed but I remember it was recommended for new lawn seeding.

"put down fertilizer and Kentucky Bluegrass seed and used plenty of both"

Define "plenty" ... because fertilizer can KILL plants if you use in in excess.

What did the package instructions say, and what did you actually do?

Also, please remove the red plastic contraption. It is going to kill the grass underneath if it sits there too long. Just my 2 cents of advice. LOL.

"The area that grew the best is the area that sees the most shade"

To me that is saying you are not keeping the rest of it moist enough or the conditions are too hot. That said, KBG will sprout in the shade but will not do well in it, like J Watson has mentioned. You would have been better off with a cool season blend.

What's the drainage situation? I bet the water near the house flows into the spot that doesn't have grass growing. Does the ground continue to flow down into the grassy areas beyond? If the grassy area on the left is higher than the grassless area in the center, the grassless area could just be water logged. That will rot seeds and the roots of anything in there. Hard to tell from the photo but the soil looks very soggy and it looks like it as been eroding.

I was watering the area twice a day for a month, except on days where we got a lot of rain.