Repository: create-react-app
Issue: react-scripts 5.0.0 build does not split resulting JavaScript bundle
Labels: needs triage,issue: bug report

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### Describe the bug

After upgrading the `react-scripts` package from 4.0.3 to 5.0.0, the `react-scripts build` command only produces a single JavaScript file, where previously there were 3 files. Because of this, the resulting `.js.map` file is too large for us to version-control. 

### Did you try recovering your dependencies?

I have run the commands side-by-side in different copies of our source repository and confirmed that the RS 5.0.0 code is not producing comparable results to 4.0.3. In both trees, I was running against a clean re-install of all dependencies (removed `node_modules` and re-ran `yarn install`).

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### Which terms did you search for in User Guide?

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I searched for "code splitting" and read the section on it. It implies that code-splitting is based on dynamic imports (which we are not using), but the application code itself has not changed (only the build tools).

### Environment

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```
Environment Info:

  current version of create-react-app: 5.0.0
  running from /home/rjray/.npm/_npx/20562/lib/node_modules/create-react-app

  System:
    OS: Linux 4.15 Ubuntu 16.04.7 LTS (Xenial Xerus)
    CPU: (12) x64 Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz
  Binaries:
    Node: 14.18.3 - /home/linuxbrew/.linuxbrew/opt/node@14/bin/node
    Yarn: 1.22.0 - /home/linuxbrew/.linuxbrew/bin/yarn
    npm: 6.14.15 - /home/linuxbrew/.linuxbrew/opt/node@14/bin/npm
  Browsers:
    Chrome: 96.0.4664.93
    Firefox: 88.0
  npmPackages:
    react: ^16.14.0 => 16.14.0 
    react-dom: ^16.14.0 => 16.14.0 
    react-scripts: ^5.0.0 => 5.0.0 
  npmGlobalPackages:
    create-react-app: Not Found
```

### Steps to reproduce

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I'm not sure how to describe reproducing the problem, and I cannot share the project's `package.json` file as it is an internal company project.

### Expected behavior

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I expected it to behave identically to the 4.0.3 toolchain.

### Actual behavior

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When I run `react-scripts build` on the repo that has version 4.0.3, the resulting `build/static/js` directory looks like this:

```
$ ls -lG build/static/js
total 7400
-rw-r--r-- 1 rjray 1289088 Jan 19 09:11 2.1e43ba39.chunk.js
-rw-r--r-- 1 rjray    3423 Jan 19 09:11 2.1e43ba39.chunk.js.LICENSE.txt
-rw-r--r-- 1 rjray 5081380 Jan 19 09:11 2.1e43ba39.chunk.js.map
-rw-r--r-- 1 rjray  314529 Jan 19 09:11 main.38d92359.chunk.js
-rw-r--r-- 1 rjray  868002 Jan 19 09:11 main.38d92359.chunk.js.map
-rw-r--r-- 1 rjray    1559 Jan 19 09:11 runtime-main.5f8120df.js
-rw-r--r-- 1 rjray    8278 Jan 19 09:11 runtime-main.5f8120df.js.map
```

When I run the repo with the 5.0.0 toolchain, the resulting directory looks like this:

```
$ ls -lG build/static/js
total 6836
-rw-r--r-- 1 rjray 1484759 Jan 19 10:47 main.7f057cb8.js
-rw-r--r-- 1 rjray    2160 Jan 19 10:47 main.7f057cb8.js.LICENSE.txt
-rw-r--r-- 1 rjray 5508473 Jan 19 10:47 main.7f057cb8.js.map
```

### Reproducible demo

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I cannot, as this is an internal company application.

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