Why should NPM packages be as small as possible?
Most of the popular NPM packages are very small in size, as it's a crucial thing that affects the npm packages. Let's look at why it's a crucial thing:
One is the performance factor of the applications you are building. Most of the applications you are working on are to be highly performant, and should work even in low bandwidth settings.
Imagine if your npm package let's say is 10 MB in size. I don't expect 99% of users in India never load your application in web or mobile build with node_modules. But Why?
It's because loading your application will easily take 5-10 seconds, while an average application is expected to return a meaningful content load usually in milliseconds. This is why it's very important to keep your application small in size, and easily usable for a lot of folks. This is why popular NPM packages like React, moment.js are just Kbs in size.
One of the most common complaints, I heard from other folks was why to use React for a TodoList App with 3MB size when you can do the same thing easily with vanilla JS + CSS(which is in a few KBs) for a very performant reason. Any frontend framework has its pros and cons.
Also, it's very important to make your packages as small as possible to be highly reliable and cost less cost for computing required for hosting. So one of the simplest things we can do is to reduce dependencies as much as possible.
This can be done by not trying to install third-party dependencies when we are working on any application. Even though I agree a lot of stack-overflow answers recommends this approach. Yet generally the loading time is not so slow even though there are dependencies, as most of the common dependencies like JQuery which are commonly used in multiple websites are cached in the users' browser itself if they come from CDN.