I think its because for security reason. Using different bitcoin wallet is much better than to put all your bitcoin in one Wallet. We all know that nowadays lots of hacker in this world. So if incase one of bitcoin wallet is being hacked, they will not lose all of their bitcoin because they put it in different wallet.
Yes having multiple wallets will reduce the risk of loosing them as there are many hackers who are keeping close watch on our coins, so even if something goes wrong with one wallet, the other wallet will take care of our coins.
there is wallet with security alert ? i mean in case of hacking or try to connect from differents ip or place ther warn you ?