The only reason there are so many debates is to sell commercials.
That's the ultimate underlying motive but I don't think it's the direct motive.
We can't discount that it gives them something to talk about and pretend has actual importance. The media struggled to explain the Santorum Iowa victory because only a handful of people, often from smaller media outlets, knew he had visited every county, was hitting all the churches, etc. The broader "mainstream" media basically only consider the campaign to exist within the debates and any "gaffes" or interviews that occur. (And in many ways, for people outside Iowa and NH, it's how it does exist.)
Look at how "winners" of the caucuses are treated even when in many cases they're splitting or gaining little ground in terms of delegates. (Like Santorum who "won" Iowa, Colorado, Minnesota, and Missouri and secured zero delegates from those polls.) You'd think after 2008 and the long war between Hillary and Obama that people might be more interested in these things. But we're just so used to someone driving everyone else from the field in mid-Feb and nobody cares.
The Obama camp ran up a good number of delegates in 2008 by making sure that they got actual delegates and not just winning straw polls and eventually getting nothing. It undermined any possible Hillary momentum because the delegates were locked down. The Paul camp is trying the same strategy, which isn't working for obvious reasons, but they are getting outsize delegate counts out of caucuses. While both Santorum and Gingrich could never run a true national campaign against Romney because they didn't even have campaign offices or anything in many of these places. Santorum didn't even get delegate candidates into tons of places in Ohio. He could have got 75% of the vote and still walked away with only a third of the delegates because they failed at planning. Both the Romney and Paul teams were the only ones to plan for any long slog. It's amazing that they were the only ones who even got on the Virginia ballot.
Hell, it's how McGovern got the nomination in the first modern primaries, he knew the rules because he basically wrote them. (Although he, and Carter, also gave Iowa its importance.)
Nobody actually wants to know how the caucuses and nominating processes work. Plus they're going to support the candidate anyway. Nobody would want
*x* to get into office, destroy the economy and embolden the Iranian terrorist hordes.