Often, sarcasm is used to deflect, to avoid what lies beneath. For Twain, it served to reveal what lay beneath, to cut through the shiny surface, not thicken it. That's wit, I think. When you wince when you read it, not when you ROLFMAO.
It's hard to be open to that. Usually if wit is the purpose, it ends up being watered down to be PC or whatever. People who speak their minds sharply like Twain and Cronkite are rare, especially today. Snark is what's replaced them, the offhand quips that people trying to be smart without paying attention throw around designed as a response without substance.
I draw or paint dots on a page or vinyl record. There is no actual depth. It's an illusion, if I've done it right, that somebody's there. An illusion that's damn hard to create and then not screw up.
Why would you WANT to glance off the surface when there IS real depth below? Life's too precious to just give it a glance.