We must follow this model because no one owns the web. In grocery stores we buy items in bulk. We do not buy them one at a time. Servers are just the same. Good performance requires course-grained communication.
Servers have only a limited ability to multitask.
A server cannot run more and more tasks. This is like having only so many cash registers in a grocery store. Even queues run smoothly until some problem task surfaces. For example, checkout clerks get interrupted to do a price check and the entire system experiences a slow down. Servers, like a grocery store, need interruptible models.