game of thrones - Does anyone ever explain why no one in the south cares about the Wall anymore?

According to this answer, The Night's Watch gets it's funding from The Gift, which is comprised of taxes taken from towns and villages near the Wall, I always assumed they were funded directly by Winterfell or perhaps even all of the kingdoms contributed in some way, a collective Wall Tax or some such.

If the Wall is there to keep Wildings out, and everyone knows the Wildlings are behind the Wall in fact the Wildlings are constantly raiding south of the Wall, which is why there is no one left for the Night's Watch to tax, why then does no one fund it?

If the Wildlings overrun the Wall, it's bad news for everyone in the south.

I've read the books and seen the shows but I can't remember if anyone ever explains why no one funds the Wall.

Is there ever a reason given?

It's pretty important but no one seems to care about it.

Answer

The wildlings have invaded the Seven Kingdoms several times. Every single time, they were crushed before they even reached Winterfell. Typically, they were crushed by the Starks of Winterfell, in their capacity as Warden of the North.

Simply put, the wildlings pose no threat to Highgarden, to Casterly Rock, not even to the Riverlands just below the Neck. So right off the bat, the vast majority of the Kingdoms have basically nothing to gain by sending aid to the Night's Watch, other than ridding itself of criminals and mouths to feed.

But even Northerners see the wildlings as more of a nuisance than an existential threat. As Jon tells Ygritte, Mance Rayder's undisciplined army is bound to lose to the discipline and military tactics of the Seven Kingdoms.

He's ultimately proven right when Stannis' force of 1,500 completely decimates Mance's host of 100,000.

Even Ned, who is very generous to the Night's Watch, doesn't see Mance Rayder as a threat.

“And it will only grow worse. The day may come when I will have no choice but to call the banners and ride north to deal with this King-beyond-the-Wall for good and all.”

“Beyond the Wall?” The thought made Catelyn shudder.

Ned saw the dread on her face. “Mance Rayder is nothing for us to fear.” (Eddard I, AGOT)

So when you get down to it, the people south of the Wall neglect it because they don't see any threat that the roughly 1000 brothers of the Night Watch can't handle. Obviously, they've all forgotten that the Wall wasn't built to keep out men...