because don't put all of your money in the same bag,divide it,and when one lost,the rest still there
That's right, mostly users have many wallets because they don't feel safe keeping all their bitcoins in one place because in case if you are having all of them in one place and that gets hacked or something else happens to it then you are ruined.
Honestly i think almost all members here are using multiple wallets in many reason not only for safety of their wallet.. also they are using other wallet because of good benefits.. that you will not get in other wallet. just sample coinbase or xapo you dont need to pay for fee for every transaction unlike you using bitcoin core block chain or electrum that you need to pay for fee to send it to others.