Because PCGS overgrades their modern coins and everyone knows they can buy it cheaper with a PCGS label.
I have stated before that NGC needs to start exclusive sets that only allow NGC graded coins. There are too many sets with most or all PCGS coins in the NGC registry. This is really unfair that buy the coin and the label and are given no credit at all for this. I believe PCGS coins should have to be sent in to be CrossOver within a certain timeframe or have their points reduced to the next grade level since most would never cross over in the first place. I know because I have only a couple that crossed over and thats a very low percentage!!
Come on NGC.....lets get on board and get our own exclusive sets!