Because parents are people, and a good amount of people like to have their privacy. Your mom and dad want to walk around naked and fuck in the kitchen but they can't because your 30 year old ass is sitting on the couch in your tighty whitey's drinking Dew and playing Xbone.
That's so they can always be sureyou're not doing the hanky panky
And you won't be doing much that way. Inviting dates back to your parents place would be weird as fuck at 25, let alone 30+.
And I realize dating culture is different as well so it may be less of a consideration.
Just a) go their house b) do it a in a public place