A minor point I feel vaguely obligated to make: Sukkot is hardly a "minor holiday"; it's one of the three major pilgrimage festivals and one of the five holidays(pilgrimage festivals plus high holy days) actually mentioned in the Torah. Part of the reason you'd have trouble finding a etrog I suppose is that etrogim are rarely grown in the US and usually have to be imported.

The question you've posed is interesting though. I think there are some other factors besides it coming close to Christmas that make Hanukkah very popular. It's a mainly domestic holiday celebrated in the evening, which both makes it more similar to Christmas and means that it can be observed without really affecting the workday. It's also a relatively simple and easy holiday to celebrate compared to Sukkot(which requires some minor construction work) or Passover(a seder can last into the wee hours of the morning and keeping a kitchen kosher for Passover is a rather involved undertaking), so it's relatively easy to celebrate if one doesn't have a lot of time or Jewish knowledge. And it has a story behind it that is both easy to understand for non-Jews and extremely appealing to an American audience revolving around claiming freedom to practice one's religion(and, I suspect, which would resonate a great deal with many Americans during the Cold War who contrasted themselves with atheist Soviets). What's more puzzling to me though is Purim seemingly becoming less visible and popular; it has a similar theme and it used to be the purim balls were a very major part of the social calendar.