I've only looked at a few of the Big 12 schools, since I initially was mostly looking at AAC schools. So it's possible BYU isn't the weakest draw of those, when we consider the difference in schedule. But the general idea is accurate - on this board we tend to vastly overestimate BYU's drawing power.

Big 12 teams draw substantially more than BYU, even though we claim to play a near-P5 schedule. That's not a 2020 thing, as some have suggested, but an ongoing thing over multiple years. Even teams that play fewer marquee names (see the AAC) outdraw us, which leads to a lot of anger/disbelief, but it's data-supported.

There's a few reasons for this (here we move to my opinion, rather than data), some we can change and some we can't.
1) Being independent means that our games are largely exhibitions, especially to our opponents. BYU (with the exception of Coastal Carolina last year) hasn't played a game in 5+ years where the outcome made much difference. We're (at best) the 5th or 6th most anticipated game on every one of our opponent's schedules (and generally lower if they're a P5). The Memphis/UCF game might be a big deal for a conference title or a NY6 berth. BYU/Washington means nothing to either team beyond pride, even if Washington is a stronger opponent.

2) Being in the Western US means that many of our games are shown at a time when fewer folks are watching. Frankly not a lot we can do about this. Maybe get some more eastern rivals?

3) There's a LOT of BYU "fans" that are very casual about it. We have a larger fanbase than a lot of other schools, but I'd wager a larger percentage of them are fans in name only. If you're LDS, go to your ward and you'll see a lot of BYU fans there who couldn't tell you when a game is being played, let along take the time to watch it. This critique is clearly not directed at folks on this board, but there's a lot who aren't nearly as engaged.