Super Bowl season is here, and companies across the board are expected to spend big on memorable ads that promise to lock in more consumers. During the past few years, however, Doritos and other companies have done things differently — rather than pay ad agencies to script, shoot and test the perfect Super Bowl ad, they have relied on consumer-generated content that ask die-hard consumers to send their own 60-second spot for air before a national television audience.

The strategy has success in the past, but this Super Bowl will be the final year that Doritos will rely on consumer-generated ads. PepsiCo pep has followed, in a surprise move that has puzzled many industry experts who thought consumer-generated content made sense for several reasons.

For one, it offers a vast supply of creativity. Instead of relying on a few creative teams at an ad agency, a brand can get thousands of ideas from creative people all over the world. It seems only natural that more ideas should result in a more creative and effective final product. Secondly, consumer-generated ads encourage engagement. Brands are looking for ways to connect with customers and social media has transformed the way people communicate and interact. Consumer-generated ads open the door for brands to be part of the discussion.

Consumer-generated content also can lower costs for the right companies. Working with an ad agency is not inexpensive. Just producing a polished TV commercial can cost $1 million or more. Consumers entering a contest are working for much less. Someone looking for a career boost might create a finished spot for free and consumer-generated creative could be a low cost way of developing advertising.

The Doritos’ Crash the Super Bowl program has produced some of the most memorable Super Bowl ads over the past 10 years, receiving more than 30,000 submissions and, winning the USA Today Super Bowl ad poll three times.

Despite the benefits, consumer-generated advertising in the Super Bowl has largely fizzled out and Doritos isn’t the only one giving up. Chevrolet and Career Builder tried using the technique to create Super Bowl ads, but both brands have abandoned it.

One critical explanation is that, despite all its benefits, there are several hidden costs to consider.

One problem is that running a consumer-generated ad contest is complicated. Companies have to work out elaborate legal arrangements, paying particular attention to copyright and licensing issues. Even figuring out ownership of a particular idea can be difficult. What happens if two people send in a similar concept? Designing the program take time, money, and oversight.

Another problem is that a company can’t simply announce a contest and assume that entries will come flooding in. The brand has to market the event, letting people know about it and generating interest. This is neither easy nor inexpensive; the world is cluttered and most people aren’t looking for contests to enter. The company also has to give people a reason to participate in the event. Why should someone spend time and money thinking up and creating a piece of advertising? There has to be a benefit. This year, Doritos is offering $1 million and the chance to work with Zack Snyder, a high-profile director.

For these reasons, consumer-generated creative can be more expensive than people realize. Promoting a contest, offering a meaningful prize and working through all the executional complexity all drive up costs. Companies that try consumer-generated creative rarely walk away impressed with the savings.

The results are also questionable. Most consumer-generated creative is simply not very good. Developing a strong Super Bowl spot is a challenge; advertising professionals with decades of experience can’t consistently do it. Also, at the end of the day, brilliant advertising isn’t just about entertaining the consumer. The most effective advertising contains a strategy that taps a consumer insight and communicates it in a compelling way. The chance that someone with a video camera can, of his or her own accord, deliver both a compelling creative and strategic advertisement is likely remote.

Encouraging people to make and share videos about your brand can also be creatively risky. Someone who doesn’t like your firm might create and circulate a negative piece of advertising. An individual with poor judgment could create a video that is sexist or racist or otherwise inappropriate. Yes, the brand can apologize that the person is not an employee, but it requires damage control nonetheless. This all could reflect poorly on your brand.

Working with a team of seasoned marketing professionals is, for most brands, an easier, safer and more efficient approach to develop both compelling creative and sound strategy, especially when it comes to a high-profile event like the Super Bowl.

Tim Calkins is a clinical professor of marketing at the Kellogg School of Management at Northwestern University. Derek D. Rucker is the Sandy and Morton Goldman Professor of Entrepreneurial Studies in Marketing at the Kellogg School of Management at Northwestern University. To learn more about the Kellogg School Super Bowl Ad Review, visit here.