Card Grading Costs - what am I missing

[swarmee]

1) Up until about 4 years ago, you could get PSA grading in bulk for inexpensive cards about $6/card.
2) It's a human condition to overgrade your cards in your own mind, so people regularly submit cards they think are NM when a true result is that they are only EX 5s.
3) PSA has ebbed and flowed over the years with grading to their published standards, and people currently believe they are MUCH tougher than normal on cards from the 70s and 80s than ever before.
4) Once a card has been graded low, there's less of a demand for it, because it no longer has much "upside" (unless you're buying to trim the card and resubmit hopefully for a higher grade).

If you've been gone 15 years, recommend you read some threads over at Blowout covering the trimming scandal.
https://www.blowoutforums.com/showthread.php?t=1298835