It's because the bulk of standbys listed on these screens are non-revenue passengers (employees/and or their family/companions)... and ORD-DEN happens to be one of the most popular routes for employee travel. Much like the widebodies attract us FTers, they also attract employees.

And FWIW, these lists are generally pretty accurate. It isn't common for standby lists to be rolled over -- both revenue and non-revenue passengers have to re-list for another flight -- except in certain markets (like HNL, or flights like ORD-DEN). Obviously some standbys have found alternate means to get where they need to get -- or have simply gone home -- but their names will still show unless they cancel their itineraries...