Because Lion was distributed as an app, you can manually extract the disk image to create a bootable USB for clean installations: How to install macos using usb drive? Need help on this!

In the context of Mac OS X Lion, the ISO format was essential for two primary reasons:

Comprehensive Guide to Mac OS X Lion ISO & Installation Mac OS X Lion (10.7), released on July 20, 2011, marked a major transition for Apple by becoming the first version available primarily through digital download via the Mac App Store . While originally a paid upgrade, Apple now provides the Mac OS X Lion Installer as a free download for those maintaining older, compatible hardware. Key Features of Mac OS X Lion

Lion introduced several security enhancements that laid the groundwork for modern macOS security protocols.