Why do some big extension companies choose not to use repositories while others do

Question

We are currently installing extensions from different companies on our new M2 site.

Some companies (not gonna call names, don't know if that's allowed) just have you
composer require their repository so you don't have to manually download any .zip files, composer does everything for you.

While others, you have to download the .zip file of the extension and composer require path to the zip files.

I am curious, why companies would possibly not choose to use repositories for client convenience?

Answer 1

Because Customer A's composer packages need to be different from Customer B's. Presumably, they only want people to be able to access what they've actually purchased, and that's not a trivial problem. Most companies that don't probably lack either the size or the expertise to pull it off.

There is Private Packagist to power it, but it's expensive (billed per customer, per month).

Or they could home-grow something, either manually generating the composer repositories after each purchase (slow and a lot of overhead), or scripting the process (like Magento Marketplace does--but a lot of work to implement).

Any way about it, it's not as easy as "just set up composer", and that's why many vendors don't.