Why install additional packages which bog down my system when I can use a webapp? What about for users of machines where they lack privileges to install packages?

27MB is bogging down your system? And yt-dlp does not need admin privileges to be installed. All it needs is Python3 which is, if not ubiquitous, excessively common.

Because most people these days only own a smartphone.

Mobile?

At least here they're removing watermarks.

Now, is this a good thing? Meh. Maybe.

It almost definitely violates some sites ToS though..

But when did your mom ever need to download videos on her device when she can access them on the internet?

My mom downloads dance tutorials to her phone/iPad all the time.

My mother downloads YouTube videos as audio to put on her offline mp3 player so she can listen to music/podcasts/lectures etc. I'm sure some people are using it to download music too. There are many use cases.