every time I run docker-compose up for WordPress the DB is empty

I have docker-compose.yml file for WordPress
every time I run the docker-compose up the DB is empty and I need to run the 5 step install.

I don’t understand what I need to do.
I have a live WordPress site, I clone into my local, create the yml file.

this is the yml file.

version: '3.3'

services:
  db:
    image: mysql:5.7
    volumes:
      - db_data:/var/lib/mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: password
      MYSQL_DATABASE: '${DB_NAME}'
      MYSQL_USER: '${DB_USER}'
      MYSQL_PASSWORD: '${DB_PASSWORD}'

  phpmyadmin:
    depends_on:
      - db
    image: phpmyadmin/phpmyadmin
    restart: always
    ports:
      - '8080:80'
    environment:
      PMA_HOST: db
      MYSQL_ROOT_PASSWORD: password

  wordpress:
    depends_on:
      - db
    image: wordpress:latest
    ports:
      - '8000:80'
    restart: always
    volumes:
      - ./wp-content:/var/www/html/wp-content
    environment:
      WORDPRESS_DB_HOST: db:3306
      WORDPRESS_DB_USER: '${DB_USER}'
      WORDPRESS_DB_PASSWORD: '${DB_PASSWORD}'
      WORDPRESS_DB_NAME: '${DB_NAME}'
volumes:
  db_data: {}

Source: StackOverflow