Last night I finished Stranger Things and as I understand the so-called demogorgon is attracted to blood and that's why it leaves The Upside Down.
Why did it go to Joyce in their house?
Movies & TV Stack Exchange is a question and answer site for movie and tv enthusiasts. It only takes a minute to sign up.Sign up to join this community
Yes blood is a way of attracting the demogorgon, but it doesn't necessary mean it's the only way of getting their attention.
To the extent of my knowledge I believe Joyce's son was at the house within the upside down for quite a while. It's understood the creature is looking for Will and would explain why it was at the house too. Joyce hearing her sons voice on the phone and communicating with him with lights could put her in the firing line for attacks. Especially where the line between the two worlds blur.
For example in the final episode when Joyce is in the upside down they see the lights where she is moving much like Will. Jonathan says "Mum" and at that point she hears that within the upside down showing communication from the other side. This shows how thin the line can be between the two worlds.