It's about market size, I think, and the fact that you know more about US culture than USians know about Brit culture. If 10% of US watchers don't watch because they don't understand the culture-bound jokes, that's enough to warrant re-doing it in their culture because the market is big enough.
Brit shows are seen in their original format on certain channels. Originally only very high-quality items were imported and so there is now a very rough notion that Brit-produced shows are "highbrow". This in turn has led to a certain group of highbrow Americans reaching hard to appreciate the subtle nuance and dry Oscar Wilde-ish wit of "Are You Being Served".
