A few reasons have been pointed out by others, but let me include another. others have pointed out: - Client side SPAs sometimes don't hit server logs - Some

A few reasons have been pointed out by others, but let me include another. others have pointed out: - Client side SPAs sometimes don't hit server logs - Some static sites are hosted places where you don't have access (github pages, netlify, etc) - Bots are sometimes defeated by a simple js file But another one that is not mentioned is one that effects large apps and services. Many large apps and services don't exist on a single server. Furthermore servers are launched and destroyed on a whim to meet scalability needs. Javascript analytics easily surmount this. I suppose it is still possible to feed multiple server logs into a single source of truth for analytics, but I dont know if such a solution exists right now. JS Analytics easily overcome this obstacle.