This is a way more legit answer than "nah, you actually don't want it, even though you think you do". That one is a a bit bullshit, but this one really puts the whole thing to bed, for me.

I build websites for a living. I have some projects that have been expanding, evolving and growing for 10+ years, currently serving tens of millions of requests per month, and if I think about trying to host a "vanilla" version of the website, like the version as it was say 9 years ago... All those issues creep up. Even if I can roll back the code to that time via repo revision history, I also need to rebuild the database structure to work with the old code, I need to try and restore any image or other such data that the code requires but that might have been in the database at the time instead of the repo, I need to fix all the scripts and such that were designed to run on old versions of server software, on old versions of Linux, with different software and hardware configurations, not to mention any bugs, security vulnerabilities, etc that have been rolled in to the code over all that time, AND all the convenience and code structure improvements that have been made over the years, that the team relies on to produce quickly, which weren't there in that early version of the code, etc etc...

I know website does not equal game but really, in a lot of ways it's very similar, and probably even MORE of a mess than a website would be, to do this.

It's possible but if only a small percent of my users express interest, and an even smaller percent of THOSE users will actually use it, and then I'll also need to run and maintain it for those users going forward, even after it's all fixed and working... There's just no fucking way. Better to devote all those resources to moving forward with the product as it is today and to try and resolve any feature requests from here.

I know it already existed, with emulated servers, but it's still a waste of resources for Blizzard to build their own emulator, and I'm sure the emulated server and that version of the client had a lot of issues that people would not tolerate in a retail product. The more I think about it, the more issues I keep finding with it.

Yeah, people need to get over it. It's just neither feasible nor justifiable for Blizzard to do it.