Because 3 years ago he had played NO quarters of any pro football. And there were question marks of can he take snaps from center? learn to read defenses? go thru progressions if primary is covered? he did none of those things in college. He had 3 years of watching the goat at all 3 of those things, not to mention josh mcdaniels. and tho 6 quarters is a small sample size-it was a QUALITY sample. He played well in a nationally-televised game vs. a SB contender and one of the better D's in the nfl-on the road. And BEAT them. Are you saying he would have had MORE value 3 years ago when he had done NONE of those things?
In addition, hes a safer option than he would be as a FA-where theres a likely bidding war-and a team might overpay. Trade for him before 2017 season, you still him under contract for a year-if he plays well, then you extend him. The team that already has him has an advantage. If he doesnt play really well, you could then sign him for less. I highly doubt that he would flat-out suck.