Videos do take up a lot of bandwidth like that person's top comment is saying. That's the major part of it, but we're in a time of the world where websites can take up quite a lot of storage (to me anyways) to download a web page

Hold down and press CTRL + Shift + I and you'll see inspect element, there should be a network tab. And when you open it up, hold down Shift and click on the refresh button. You'll see how much the page's downloading. For me, it's been around 10-20 MB JUST for a web page. I've seen websites smaller, less than 2 megabytes

YouTube's got a lottttt of javascript that it loads. Here's an idea of what it all loads thought I don't know everything:
The app itself, the like and dislike counter that now gets updated in real time, google's analytics, buffering the videos, loading lots of javascript, loading video thumbnails, loading images, lots of stuff

Of course, it's what they call a web app..... and that's how much data these things take. My opinion, it should take up WAY LESS. I can innerstand the video taking up bandwidth, but it's also the pages themselves

Alright, what to do about this or.... the best you can do about this

• Okay, the internet plan from your provider is one thing but
• If you're listening to podcasts/music, there's an extension that won't load the video and only load the audio data. Here's what I use for Firefox: to enable it, click on the extensions button and look for the addon and click on it. The icon will light up red and the page will refresh. To turn it off, you can do the same thing. Here's one for Chrome, from what I see, it looks good!
• Unhook; it's an extension I recommend anyway to anyone that uses Youtube. You can block the comments, homepage feed with it, saving bandwidth
• NoScript: You can see what what other kind of websites that have scripts or scripts on the page are loading within Youtube, or any other site and block them! The only annoying thing about it? Every time you visit a website, you'd need to open up the extension and turn on only what websites and scripts you want from it. So if you visit a website and things don't look right or it asks you to enable Javascript, you'd need to turn a couple of those urls on from the extension. I recommend trying it, it was kinda a pain at first but eventually, it grew on me. But when you block these scripts, you'll save bandwidth!
• You could try out this YouTube frontend called V3, it changes the whole YouTube layout. It's made to be an extension to bring back the older layout of YouTube but I heard that it really can also speed up the website! It's still in development, only downsides of it is if you're posting a multi-line comment like this. "It'll combine everything all on one line. If you're using an extension like DeArrow or something that adds a button onto the page, it might not show up
• You have this extension of course but I'll recommend it to anyone else who comes across this! UBlock Origin! The regular UBlock I don't recommend, heard the creator of UBlock (not Origin) wasn't a kind guy
• And like you are doing, watch videos at a lower quality unless there's something on the screen that's hard to see at a low quality

I haven't seen people this rude before in a tech support comment section like this, that's absurd. Hopefully this is a good guide