That's like asking why does Windows use \ instead of /. It's not hatred, it's just... the way things work. Changing it would be very costly and would create compatibility problems for decades presumably, so why do it?
Whenever it comes to something programming-related that might improve code portability between different OSes (C99, LF, UTF-8, etc), there's a mountain of after-the-fact justifications for why it would break backward compatibility and other such tripe.
But honestly, what would making "EDIT" accept "\n" alone do to break backward-compatibility? "\r\n" would still work, of course. Is there a group of people inserting stray "\n"s alone into text files, and expecting Notepad to silently ignore them and dump all of that text onto the same line? If so, those people are absolutely horrible :P
But okay, fine. Require a program .Manifest flag to opt-in, then another special ES_ACCEPT_LF flag with a caveat that it's Windows 10+.
Even all the people that have jumped through hoops with things like hooking paste operations to transform "\n" into "\r\n" for "EDIT" ... that would still work just fine, it would just be unnecessary.
The only cost would be that there's a short time where people are trying to use these "\n" only text files on older versions of Windows. But we've been dealing with the fallout of that anyway for the past 21+ years now.
You can't possibly tell me that supporting "\n" alone is an immense burden for a company with as much money and developers as Microsoft. No, I'm sorry, but this, C99, UTF-8, things like _wfopen, WSAPoll over poll, etc are all very much intentional: they're designed to maximize vendor lock in. Microsoft doesn't want your code easily moving between Windows and Linux. Even though they're a convicted monopoly with a mountain of evidence of their abusive actions, they still have so many white knights ready to defend their actions as benign =(
CMD.EXE is -sadly- a bucket of suck.
> ...WSAPoll over poll...
Don't fucking get me started about the WinSock API. >:(
(I don't buy the "decades" bit, but I'll accept it just for argument's sake.)