We don't get to choose whether to exercise it or not.

Firstly, it's only even a possibility to begin with if either the Big 10 or Big 12 is unable to fill a spot.

Even then, it's not up to us. ESPN would then make that call, which, I agree with you, I'd hope they would.

But their priorities don't always align with ours. In particular, given ESPN's tenuous and embattled relationship with the Big 12, they may not find it a solid long-term move to give additional exposure to a team which will soon be in the Big 12 (which has a number of non-ESPN partners) when they could instead put (for example) an AAC team in there (a conference they do have an exclusive deal with).

If ESPN did choose to exercise that option then we'd be (according to these projections) matched up against Maryland. Which isn't exactly a sexy matchup but still better than Charlotte I guess. I'd rather get UTSA than Maryland though for sure