We are evolving our life in the digital era. Today building an application that also from the scratch you need a software stack in both standardized & consistent form.
For creating a robust backend, you need a set of tools that can reduce your development time & streamline resources as well. Today, we have several software stacks such as ROR, LAMP, & many others that have made the stack field crowded.
That is the reason why most developers prefer a combination of technologies to get better & faster results for mobile & web app development. MEAN Stack is the best example of that kind of technology.