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 online services category. There are more than 25 alternatives to Google Lens for a variety of platforms, including Web-based, Android, iPhone, iPad and Google Chrome 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 NormCap, CamScanner, PimEyes and PicMenu.
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.