There is a lot of corporate crap that makes the front page, I expect that reddit receives remuneration for this. e.g. there was a front page post recently of a TacoBell sign that was 20 years old, a crap post with little value, but it ends up with +2000 votes and is front paged on a friday(i think). What do you think that sort of exposure is worth to Tacobell? If Tacobell did pay for some product placement of this nature do you think reddit would ever tell its users? Nope, that would pretty much kill any future attempt to do this sort of thing.
Whether the Tacobell payment is official or hidden by way of increased ad costs on other CondeNest properties or even if it is offered as a sort of add-on to their usual advertising in print media. Reddit is selling their front page one way or another becuase it is pretty much their cash cow, however milking it must be done very carefully because a user backlash would kill the site or future opportunities to monetise in this manner.