Here is how ThinkProgress has summarized this completely counter-intuitive situation:

There is some drama surrounding this upcoming event. And it has to do with the
debate’s location — the University of Colorado Boulder, or CU-Boulder.

Since September, there’s been an twinge of animosity among some students who claim they were misled about what housing a presidential debate on campus would be like. They thought they would be getting an unique education in American politics, but instead, some say they’re only getting a lesson in marketing.

“’The college framed [this debate] as a real chance for the students to have this meaningful political experience,” said CU-Boulder student Aaron Estevez-Miller, 21, in an interview with ThinkProgress. “In the months since then, the university and chancellor have really failed to deliver on this promise.”

The controversy goes like this: Wednesday’s debate is to be held in CU-Boulder’s 11,000-seat Coors Event Center, and students expected some seats would be open to some of the 30,000 university students. Instead, the Republican National Committee and CNBC originally made only 50 tickets available to the community—that’s including faculty, university board members, and a select few number of students. (On Monday, under pressure, the RNC increased that number to 150.) And the majority of those select few student are from majors like political science and economics, Estevez-Miller said.

The University and the RNC had justified this by noting that most of the space in the arena will be taken up by cameras and the CNBC broadcast team. This is commonplace—At the first Republican debate in Cleveland, only 4,500 attended, though the Quicken Loans Arena seats more than 20,500. But to Estevez-Miller and his group, Student Voices Count, school officials are using the debate as a marketing opportunity.

“They’re sacrificing young people’s political experiences to the arbitrarily defined benefit of media value and exposure,” he said. “People here are voting in their first presidential election—it’s important that they have a meaningful experience with American democracy, and [the college] is not leaving that impression on young people.”

Estevez-Miller does not go as far to suggest that the school or CNBC or the Republican National Committee are trying to keep students out for political reasons (he emphasizes the Student Voices Count is non-partisan). But it has been suggested by the fact that progressive politicians and groups have joined the call for more student participation. ProgressNow Colorado is calling for at least half of the seats to be made available for students, and while it doesn’t say it outright, its recent press release seems to accuse the Republican candidates of being scared of the progressive student body.
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Here is that press release from ProgressNow Colorado:

Nothing Less Will Do: 1,000 GOP Debate Seats For CU Students

FOR IMMEDIATE RELEASE
Tuesday, October 6, 2015
CONTACT: Amy Runyon-Harms, ProgressNow Colorado at 303-870-0448

DENVER: As controversy continued to grow over the lack of seats made available to University of Colorado students for the Republican presidential debate at the Coors Events Center on October 28th, progressive and student advocacy groups joined with CU students to request an additional 1,000 seats in the 11,000 seat capacity venue be made available to students.

“I was excited to learn that the Republican presidential candidates are coming to my campus,” said Spencer Carnes, a University of Colorado undergraduate student. “But when I found out that most of the seats in the Coors Events Center will be empty, and that students had almost no chance of actually seeing the debate in person, I was offended. If politicians want to use my school as a backdrop, we expect them to let us be in the room to hear what they have to say.”

“We’ve heard loud and clear from students at the University of Colorado that they expect better,” said Amy Runyon-Harms of ProgressNow Colorado. “There is tremendous excitement about holding such an important event on the Boulder campus, but shutting the CU student body out of the debate sends the wrong message. There are thousands of CU students from all walks of life who want to hear from these candidates, and there’s no reason why they can’t be accommodated.”

“No one on our campus buys this excuse that they can only handle 1,000 people at the Coors Events Center,” said Dylan Robinson-Ruet, a CU student. “If the debate is only for TV, why hold it in a basketball stadium? If they can accommodate 1,000 hand-picked attendees in a stadium that seats 11,000, they can certainly handle 1,000 more for CU students who want to be there. In fact, it’s the least they can do.”

“This is about misusing the reputation of Colorado’s flagship university,” said Runyon-Harms. “We support hosting this important debate on the University of Colorado campus. But using CU to boost the credibility of these candidates while excluding CU students from participation in this debate is simply wrong. It’s time for debate organizers to do the right thing, as we’ve called for from the beginning, and make 50% of the seats at this debate available to CU students. That means making 1,000 more seats available to CU students in addition to the 1,000 seats already spoken for.”

“If the GOP refuses to allow students to even attend a presidential debate on their own campus,” asked Runyon-Harms, “what does that say about the candidates?”