I don't know why UA is the most popular forum on FlyerTalk. Questions: Is UA the largest airline in the U-S? That could be one reason.
Also, Are there more Frequent Flyers in UA
than other programs? That's another possible reason.

It seems at least more than half of FlyerTalk members are a member of UA Mileage Plus. Plus if you include The Star Alliance link, UA's nationwide network of flights I could see several more reasons why UA gets a lot of responses.

Plus those "delicious" Mustard Pretzels!
CATMAN