People wear suits to be buried. Why?*
I don't want to be buried in a suit.
I actually want all my suits to be cremated when I'm dead. Or sooner.
And not just mine. Everyone's. While they're wearing them.
At least the tie probably doesn't cause any discomfort when you're dead.
You certainly never see any angels wearing ties.
Ancient Egyptians, that's another story.
They would be buried with their best outfit, plus all their other outfits (you have to be prepared for all kinds of afterlife weather, plus different afterlife occasions), their money (hope the currency exchange is favorable between life and death), belongings, pets, slaves, you name it.
(Or maybe don't name it, because that might make you feel worse for enslaving it.)
Certainly, if ties existed, they would have worn them. All of them.
Pharaohs were like the first boy scouts, except with not as much gaudy jewelry.
I'm actually a little surprised that more modern American celebrities don't pharaoh it up when they die.
Though with botox and face lifts and other plastic surgery essentially being on par with getting oneself stuffed, people are indeed preserving themselves in a beautiful death-like form while still alive.
* Possible answers:
To show people you're a classy dead guy?
To make people angry because they're not as dressed up as your body?
To waste a tailor's time?
Seriously, why not just half a suit?
The half that's visible to the viewers of the open casket.
That way the tailor could save on fabric.