Why are internet upload speeds so much slower than download speeds?

Uploading data tends to be much slower than downloading, and it turns out there's a very good explanation for it.

Uploading data tends to be much slower than downloading, and it turns out there&#39;s a very good explanation for it.<p><img src="https://www.engadget.com/img/gallery/why-are-internet-upload-speeds-so-much-slower-than-download-speeds/intro-1791899938.jpg" /></p>