ngOnInit not being called when Injectable class is Instantiated

Why isn't ngOnInit() called when an Injectable class is resolved?

Code

import {Injectable, OnInit} from 'angular2/core';
import { RestApiService, RestRequest } from './rest-api.service';

@Injectable()
export class MovieDbService implements OnInit {

    constructor(private _movieDbRest: RestApiService){
        window.console.log('FROM constructor()');
    }

    ngOnInit() {
         window.console.log('FROM ngOnInit()');
    }

}

Console Output

FROM constructor()

Lifecycle hooks, like OnInit() work with Directives and Components. They do not work with other types, like a service in your case. From docs:

A Component has a lifecycle managed by Angular itself. Angular creates it, renders it, creates and renders its children, checks it when its data-bound properties change and destroy it before removing it from the DOM.

Directive and component instances have a lifecycle as Angular creates, updates, and destroys them.

I don't know about all the lifecycle hooks, but as for destruction, ngOnDestroy actually get called on Injectable when it's provider is destroyed (for example an Injectable supplied by a component).

From the docs :

Lifecycle hook that is called when a directive, pipe or service is destroyed.

Just in case anyone is interested in destruction check this question:

Adding to answer by @Sasxa,

In Injectables you can use class normally that is putting initial code in constructor instead of using ngOnInit(), it works fine.