The OP is saying that given BYU's recent winning percentage, it's baffling that Bronco Mendenhall hasn't had a single BCS/NY6 appearance (and that winning percentage is not everything). Look at BYU's neighbors:

BCS/NY6 appearances (starting with 1999)
24 -- Georgia: 3
25 -- BYU: 0
26 -- Missouri: 0
27 -- Penn State: 2
28 -- West Virginia: 3

Given that list, it's reasonable that BYU fans should feel like they should've had at least 1 or 2 BCS/NY6 appearances in there.

But if you do the same comparison for Boise/TCU

1 -- Boise: 4
2 -- Ohio State: 12
3 -- Alabama: 7
4 -- Oregon: 7
5 -- LSU: 5
6 -- Oklahoma: 9
7 -- TCU: 3
8 -- USC: 7
9 -- Wisconsin: 5
10 -- Florida State: 9

It looks like BSU/TCU should've had at least 3-4 more BCS/NY6 bowl games each. Granted, in their cases, the blame is put more on systems that made it hard for BCS busters / their own SOS rather than on-field performance. But they should be frustrated at how few BCS/NY6 games they've had relative to their wins. Make sense?