So you're supposing they were just trying to see how far they could get into the Capitol for what purpose? Fun? Lore? A game?

Nobody else is contending that the Capital is a "round" of capture the flag. You just brought that up for some bizarre reason. The timing of this directly lines up with when they were working to count the electoral college votes. More than a few people were violent toward the cops, and nobody has any reason to believe that they wouldn't have killed some Democratic congresspeople or Pence if they had been able to find them. At least one person did kill a cop and a dozen other cops were injured.