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.
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.