A few things:
UNL makes BANK in the Big Ten. It's not only an athletic conference, it's a highly collaborative academic conference. The Big Ten Academic Alliance (formerly the CIC) opens doors to billions of dollars in grants that Nebraska would otherwise have no access to. If that was the only benefit to being a member of the Big Ten, it would be a no-brainer to stay.
Nebraska Athletics make BANK in the Big Ten. Our revenue skyrocketed since joining the conference. It's allowed us to build up our athletic infrastructure, with new facilities for basketball, track, soccer, volleyball, football, gymnastics, and with planned upgrades to several other sports in the upcoming years.
The Big XII is a garbage conference. It's not the conference we left, and it's not remotely as prestigious as the conference we're in, nor does it make any money. The Big XII doesn't want us any more than the Big Ten wanted us in 2010. The only reason that enthusiasm has soured on either side is because of Nebraska's own piss-poor performance on the field.
The Big XII is not the Big 8, and it will never be again. Those days are gone and will never return. Colorado is gone, Missouri is gone, even Texas A&M is gone. And they've replaced those good teams with... West Virginia and TCU? Ugh. No, thank you. I'd rather play in a conference with Wisconsin, Iowa, Ohio State, Penn State, Michigan, Michigan State and Minnesota.
Anyone pining for the way things used to be needs to disabuse themselves of that notion. It's never coming back. Oklahoma chose Texas as their rival and that will not change with the return of Nebraska to the Big XII. Iowa State, Kansas and KSU will still hate us and will work against us as much now as they did during the formative years of the Big XII. They are not our friends and they do not have our best interests at heart. The ONLY reason they want us in their conference is we travel to their stadiums and they get a payday when they host us. Period.
Go independent? Eh. Maybe. Again, we'd lose out on access to the CIC, which will hurt the school (and let's remember that UNL is actually a
school, not a sports factory). We'd have to figure out a contract that will replace the money we're getting from the Big Ten's GOR, which will be pretty damned hard coming off of three straight losing seasons. We are not a marquee name anymore, so we'd be negotiating from a weak position. We'd have a greater variety of opponents, but we'd also have pissed off not one but two of the G5 conferences, so scheduling those teams would be a difficult task. This is the least likely and least beneficial option for Nebraska, by far.
So... that's just off the top of my head the problems with leaving the B1G. I'm sure others have more in-depth thoughts.