Why does node.js complain about dev dependencies in a docker container?

Question

Node.js

here is my dockerfile

FROM node:14-slim

WORKDIR /class_attender
ENV NODE_ENV production

COPY package.json /class_attender/package.json

RUN npm install --production

COPY .env /class_attender/.env
COPY . /class_attender

CMD ["npm","start"]

EXPOSE 8080

here is the .env

BASE_URL=http://localhost:8080

MONGODB_URI=mongodb://localhost:27017/test1
SESSION_SECRET=Your Session Secret goes her
OPENSHIFT_NODEJS_PORT=8080

when I try to open a docker container, it gives out

Error: Cannot find module 'morgan'
Require stack:
- /class_attender/app.js
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:885:15)
    at Function.Module._load (internal/modules/cjs/loader.js:730:27)
    at Module.require (internal/modules/cjs/loader.js:957:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at Object.<anonymous> (/class_attender/app.js:5:16)
    at Module._compile (internal/modules/cjs/loader.js:1068:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)
    at Module.load (internal/modules/cjs/loader.js:933:32)
    at Function.Module._load (internal/modules/cjs/loader.js:774:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12) {
  code: 'MODULE_NOT_FOUND',
  requireStack: [ '/class_attender/app.js' ]
}
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! [email protected] start: `node app.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the [email protected] start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

What am I doing wrong? Is Node.js supposed to ignore dev dependencies?