It's because some gambler's doesn't want to go out, and would rather play at home online.

As for the question, it's really hard to answer, we can just have our own speculation on it. I have played both though, but still can't tell the difference if games are being rigged or not. Maybe others says that it's online because after all we have seen some videos on it. Recently, I saw one, but I will not want to put it here as it's one of the most active casinos here. Dealer is seen changing the cards, you have to see it for yourself how cheating is in front of the mirror. And for sure this dealer might have been fired on the spot for doing the obvious cheating.