Now that you mention it, you are right. I also did that before. because one of the wallet I have do not accept bitcoin from gambling sites. It work out for the best because now my funds are more secure.
There are lots of reasons to consider from different people on why they do have multiple addresses. As you mentioned you use other web wallets because there are really some local wallets which is very strict regarding their rules because they would block you eventually if they know that you are earning it on a particular gambling site .
Yeah there are lots of reasons why using a lot of wallet, I think including it could actually be they have cloned account, or separate income from several different sources, or avoid a hacker in order not to keep too much money in one wallet and could be the reason every wallet will surely be disrupted, so save on many of the wallet is a good choice.