Android allows adb install over usb and still sandbox the application. Sandboxing is a feature of the OS and not the store. What's missing from parent description is the publisher signature to retain allowed permissions after upgrades, which still is a feature of the OS and not the store.

Stricter sandboxing makes it more difficult to fingerprint the user and lessens the burden and dependency on legal contracts and policies. Which is what Apple just did by blocking the access to unique device id.