But even Blizz couldn't reliably make maps using their internal tools that kept Reaper where he was supposed to be.
I think that's the key -- if the tool allows you to harm the user's computer in some way, then it's not a tool you can really release without polishing a lot more, to prevent the failure modes. And it's particularly bad if it's hard not to mess up.
they said the tools are too tightly integrated into their authoring and content delivery systems
if you watch a couple of videos where they reveal how it all works: this excuse seems plausible
So Valve hires Icefrog, makes an IP claim for the dota name, all the characters, and starts creating dota 2. It felt like a "oh, I'll have this". It didn't feel right at all at the time. Still doesn't. Nothing was ever said for the community that formed around creating and enjoying the game in the first place.
Also a nitpick there have been more maintainers than those three they were the major ones for example the original developers of Dota Allstars Meian and Madcow. Guinsoo worked on the game for around 2 years until early 2005 and then Neichus took over and worked jointly with Icefrog who became the lead after Neichus left.
Main source: https://assets.documentcloud.org/documents/3726401/Blizzardv...