Зачем использовать router-outlet для доступа к компоненту другого модуля, не нужно добавлять в экспорт

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';

import { AppComponent } from './app.component';
import { HelloComponent } from './hello.component';
import { M1Module } from './m1/m1.module';
// import { AppRoutingModule } from './app-routing.module';

@NgModule({
  imports: [
    BrowserModule,
    // AppRoutingModule,
    M1Module
  ],
  declarations: [AppComponent, HelloComponent],
  bootstrap: [AppComponent]
})
export class AppModule { }


----------------------

@NgModule({
  imports: [
    CommonModule
  ],
  declarations: [
    Comp1Component,
    Comp2Component
  ],
  exports: [
    Comp1Component
  ]
})
export class M1Module {}

<hello name="{{ name }}"></hello>
<p>
  Start editing to see some magic happen :)
</p>


<app-comp1></app-comp1>

import { AppComponent } from './app.component';
import { HelloComponent } from './hello.component';
import { M1Module } from './m1/m1.module';
import { AppRoutingModule } from './app-routing.module';

@NgModule({
  imports: [
    BrowserModule,
    AppRoutingModule,
    M1Module
  ],
  declarations: [AppComponent, HelloComponent],
  bootstrap: [AppComponent]
})
export class AppModule { }

/*****************************************************/

import { NgModule }             from '@angular/core';
import { RouterModule, Routes } from '@angular/router';

import { Comp1Component }   from './m1/comp1/comp1.component';
import { Comp2Component }   from './m1/comp2/comp2.component';


const routes: Routes = [
  { path: 'comp1', component: Comp1Component },
  { path: 'comp2', component: Comp2Component }
];

@NgModule({
  imports: [ RouterModule.forRoot(routes) ],
  exports: [ RouterModule ]
})
export class AppRoutingModule {}


/*****************************************************/

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { Comp1Component } from './comp1/comp1.component';
import { Comp2Component } from './comp2/comp2.component';

@NgModule({
  imports: [
    CommonModule
  ],
  declarations: [Comp1Component, Comp2Component],
})
export class M1Module { }

<hello name="{{ name }}"></hello>
<p>
  Start editing to see some magic happen :)
</p>

<!-- it's need to use export -->
<!-- <app-comp1></app-comp1> -->

<!-- it doesn't need to use export -->
<router-outlet></router-outlet>