Because you may have enabled Encrypted and Password Protected in the security section of the mobile version of the BlueWallet App, thus making the security level stronger if one day the Android or Iphone is lost...
You should always password-protect and encrypt your wallets if given the choice or abandon clients that don't offer such services. But it isn't that important in this case because no coins can be stolen, with or without passwords and encryptions.
Today, we are announcing that the Lightning node, Lndhub.io, where BlueWallet provides Lightning wallets to its users, is sunsetting.
Too bad. This was a decent custodial service for the Lightning Network although I read that people weren't really pleased with the fees and that the routing didn't always work. As the blog post highlights, the custodial service will shut down, but users can still host their own nodes and continue using the Blue Wallet with the LN.