Yes it's hard to imagine what all that code's doing.
But I'm currently at a very small fintech, and I've got about half a million lines of code checked out. There is a lot of copy-pasted code, but I also have nowhere near all the repositories checked out.
I work on a trading desk at a financial firm. I just checked out all our applications, and they total 388444 non-comment lines of Java, 73889 of JavaScript, 13619 of Python, 9160 of C++, and some other things. The JS probably includes some vendored libraries. Also, this is just apps - we have a bunch of libraries used across our apps which will add tens or low hundreds of thousands more lines, but i have no systematic way to check them out, so i can't tell.
But I'm currently at a very small fintech, and I've got about half a million lines of code checked out. There is a lot of copy-pasted code, but I also have nowhere near all the repositories checked out.