When people are entering the community they often do not want to get voice communication (although its getting more and more common to get it as gaming gets larger). A lot of new players who post on forums say "no mic, no ts3" - so without recon, the necessity is even less than already is, so it'd make it less likely people would be forced into getting it. DP has never been that big of a strategy and teamwork game, a good player can single handedly 1v3. I wouldn't bother using TS3 anymore for matches if this were the case, I much rather listen to music.
In regards to flag fights - I'll give an example. Score: 45-44, 1 vs 1, no recon, the team with 45 grabs first - he can go hide. If he's hiding, there's no way he can be reconned. Therefore, the person who grabbed second must sit around base, or on flag, and peek at spots, hoping that the flag carrier doesn't randomly run in from another point. It would be a huge risk for the person who grabbed second to make any sort of play. So now, revives happen, he's stuck on their flag, he gets revived, games over. WITH RECON, the same scenario can be overcome. With the speed of the game and amount of paths maps have, recon is essential. The game evolved into a game that revolved around recon. The maps are generally made for recon, as that's how they've always been played. Also, juking recon is an efficient strategy to outplay people. Recon servers as a big reason the game play is not stale.
Others don't allow it because they are different games with different communities, different play styles within the game, different history to the game. In comparing games, this is the last of the things that would come to mind as a reason they are successful. Games that are currently successful would be equally successful if they allowed you to recon your opponents. It's something that people get adjusted to, and doesn't actually negatively or positively affect the gameplay, it just makes it different. DP's maps are constructed in a way where recon is needed.
Sure, the servers will probably go unused, unless two NA teams want to try it out. But I don't see people liking it, for the simple reason that the average person hates big changes to something they previously liked. It can be seen with League of Legends as well, every new season people are complaining - but by mid season nobody even remembers what got changed. People don't like change, but if they like the game they can deal with any changes over time.