Why Post the Ten Commandments?

Inspired by Eugene Volokh, I note:

Only three are currently enforced: #6 "Thou shalt not kill", #8 "Thou shalt not steal" and #9 "Thou shalt not bear false witness against thy neighbour".

We used to take others seriously: #4 "Remember the sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work..." Yeah, right. I'm old enough to remember most places were closed on Sundays, but even then restaurants were open. Similarly, #7 "Thou shalt not commit adultery" used to be a big deal, but not any more.

Did we ever make laws regarding #5 "Honour thy father and thy mother..."?

The First Amendment would prohibit the government from enforcing #1 "Thou shalt have no other gods before me" as well as #3 "Thou shalt not take the name of the LORD thy God in vain."

I'm not sure which is more contrary to current American life, number ten or number two. #10 "Thou shalt not covet thy neighbour's house [etc.]" Coveting is pretty much the way of life for most Americans. Even if the Taliban would go for #2 "Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth. Thou shalt not bow down thyself to them, nor serve them..." Pictures and other likenesses of living things have been acceptable for centuries, even among most Christians.

So the question is, why post the ten commandments in court houses if over half of them are irrelevant to modern American life? On the other hand, if they're irrelevant, who gives a good god damn, I wish I had that car.