Because it's a custodial product pretending to be Bitcoin
At least Venmo tells you they hold your money for you
Discussion
Is it really pretending to be non custodial?
From the FAQ
“Wallet of Satoshi is a mobile app for iOS and Android that lets you send and receive Lightning payments.
It is a zero-configuration custodial wallet with a focus on simplicity and the best possible user experience. It can be downloaded using the links at walletofsatoshi.com
Simply download and install the app and you are on the Lightning Network!”
They're not pretending to be non-custodial but many people use it and pretend they are using Bitcoin