Because they are competing against, older, better version of the same product, at the same price point, except it's better, and has heritage.
1972 Gibson Les Paul Custom Black Beauty w Case | eBay
This thing is so sexy.
In my experience, the early '70s was the low point for Gibson's quality control. 1972 was before they started doing the pancake bodies, I believe, but often you'll see some slapdash work from that period.
The '68 and '69 reissue LPCs have acquired a certain cache among collectors because they were supposedly made from leftover '50s blanks. I don't believe that for a minute. Gibson probably had a few of those laying around, but not enough to truly start up production again.
The thing with early '70s LPCs selling for high dollars is just pure bullshit, though.