Manually building the plugin does not copy dist/* to root

[SanskritFritz]

I am not very knowleadge in the area of web development and so. But here's what I have tried based on the documentation.

cd .obsidian/plugins
git clone https://github.com/eatcodeplay/obsidian-simple-table-math.git
cd obsidian-simple-table-math
npm install
npm run dev

I expected main.js to appear in the plugin root folder, and I can see the code for that in esbuild.config.mjs:

			const vaultPluginPath = process.env.VAULT_PLUGIN_PATH;
			if (vaultPluginPath) {
				try {
					await Promise.all([
						cp('dist/main.js', `${vaultPluginPath}/main.js`, { overwrite: true }),
						cp('manifest.json', `${vaultPluginPath}/manifest.json`, { overwrite: true }),
						cp('dist/styles.css', `${vaultPluginPath}/styles.css`, { overwrite: true }),
					]);

I issued the command console.log(process.env.VAULT_PLUGIN_PATH); in the debug console in Obsidian, and the result was undefined. I'm not sure if this is correct can you please help me why this happens?