Docker allows you to run multiple workloads on the same machine and have them all share a kernel while each having their own segmented user space so it's much less likely that processes will be able to interfere with each other. This is important for both the security and stability of the system and is similar to BSD Jails with the advantage of not being restricted to that operating system.
Running multiple heavy VMs which segment system resources gives you even better and more complete separation at the cost of being very performance intensive. The industry by and large has opted for containers as a compromise between reasonable separation and performance.
Also as Docker grew in popularity there has been an ecosystem of tooling built around it for container orchestration, image repositories, and development that make it worth using just to get access to the tooling that surrounds it.
Running multiple heavy VMs which segment system resources gives you even better and more complete separation at the cost of being very performance intensive. The industry by and large has opted for containers as a compromise between reasonable separation and performance.
Also as Docker grew in popularity there has been an ecosystem of tooling built around it for container orchestration, image repositories, and development that make it worth using just to get access to the tooling that surrounds it.