The simple answer to this is that the USOC is a single-elimination tournament. No one will ever argue that in 1991 University of Richmond was a superior basketball team than Syracuse, but, guess what? For that particular game they were better...and that's all it takes. The rest of your questions, well, they would be best asked of the ownership/coaching staff of those other teams. For the Union, they take it seriously, and I'm glad they do. It is a trophy that carries history and prestige, and the CCL spot it offers is a HUGE prize.
For me the Cup format is the best for capturing the unpredictability of sports and so it comes with excitement and potential of it's own. If you don't like it, fine, but you probably shouldn't like the playoff system, either.
I, for one, love the history of the Open Cup. Having been gone on for over 100 years, it is one of the few remnants of history, tradition, and legacy we have for soccer in this country.
I think it would be a lot less exciting if they experienced success before. It's the attempt at the first trophy. Let the people have their fun.
Chicago vs Union happens because the Open Cup is weird. Any team can win a one-off game. I suppose for the first round most teams play the "B" team because its against tier II teams, but after that its generally a decent effort lineup wise. If you don't honestly think marching into RBA on a Tuesday afternoon and beating what was very much their "A" team with 10 men in a do-or-die situation isn't something to be proud of...I really don't know what to tell you. That game is something we are going to talk about for years. And even if it was a "B+" team vs DC, they were still down 1-0 while playing with 10 men against professionals. Winning that game took some legit grit. And even if you overlook the above -- the bottom line is that the winner goes to CONCACAF. That alone, by itself, makes it important. The Union will be playing games that matter in other countries. They might even play somewhere as crazy as Estadio Azteca. I might have an insane Mexican throwing a beer cup of urine at me in a fit of rage and hatred. They will have the opportunity to play into Club World Cup! How awesome would that be?
this whole time Nick Sak was just building a tournament team.... just wait, a year from now we'll beat America for the CCL title, and then we'll beat Barcelona for the CWC title. CALLING IT NOW.
It's not the fault of the Union or the Fire that the "better" teams didn't feel like putting out their best players for the Open Cup. Also, as someone else said, it only takes one game. Upsets happen all the time. Sometimes USL or NASL teams manage to beat MLS teams in the Open Cup, does that mean that they're better teams or that the USL and NASL are better leagues? Given the Salary Cap in the league and the player roster restrictions, MLS teams sometimes have to choose which competition they feel the need to take "seriously" if your team is doing very well during the season, you tend to focus on the playoffs, supporter's shield, etc. However, if your team isn't doing well, you focus on the Open Cup.