Google Lens is described as 'Lets you search what you see, get things done faster, and understand the world around you—using just your camera or a photo' and is a popular image search engine in the photos & graphics category. There are more than 25 alternatives to Google Lens for a variety of platforms, including Web-based, Android, iPhone, iPad and Android Tablet apps. The best Google Lens alternative is TinEye. It's not free, so if you're looking for a free alternative, you could try TinEye or OSS Document Scanner. Other great apps like Google Lens are Search by Image, NormCap, CamScanner and PimEyes.
Because it is not an app but a browser extension. Can't run on Android because most browsers don't allow to install extensions on Android with few as expections.