I didn't say "a" deb repo, I said "the standard debian repository". Just like when I'm talking about NPM, I'm talking about the main NPM repository, not my company's private NPM server.
How many NPM repos are there? Just one, too-big-to-fail, centralized repository.
Don't ding apt/deb just because people setup their own repos rather than put all the code in the world into one bucket.
There's a lot more inconvenient things than adding the /etc/apt/sources
There are actually plenty, it's just that they're usually found on-prem at a company.