When the Warcraft3 map maker came out people did not have access to game engines. You either worked for a company that licensed one or you paid the 50k+ they where asking per license.
People back in the day had nothing better to do so they learned the editor and started to pump out custom games.
Blizzard noticed that there was a community forming around their map maker so they naturally moved to limit the rights of the map makers by changing their terms of service.
If you limit and suppress the freedom of the users who add value to your game, those users will simply adjust to your will, they will not leave your platform because reasons…
In 2010 Starcraft2 come out with a much more powerful map editor. The standard maps got ported and development halted.
I can assume that there where a few reasons why this happened.
One) Starcraft2 did not give the map creator the freedom to simply share his map on his website. It was expected that the creator would upload his map to the Starcraft server and players would download it from there.
This made the map maker feel that they had less control over their map and may have pushed away people from the mod scene. Why would I spend time creating something if I don't even get the social reward of a community around my project?
Two) Compared to warcraft3 Starcraft2 did not have a variety of art assets. In Warcraft you had art such as wood pick ups, giant rock monsters, icons, trees, gold mines and many many other lore elements that allowed the map maker to create something that was expressive of their idea. In Starcraft the lore elements where much more limited due to the game being an "e-sport" and lacking gameplay elements in favor of simple, easy to understand gameplay
Three) Android Store came out in 2008, two years before Starcraft2. All of the people who wanted to both make games and make money on their simple games moved over to android and started making their video games for phones
Four) Unity was release in 2005 it became an engine for indie developers and drove more people away from the modding scene
Because modders these days will not work for peanuts. Blizzard has essentially given up on the modding community to add value to their games and instead use youtube lets players to help them add value.
Lets compare a youtube lets player to a modder:
To start modding you need at least a four years of schooling in programming and at least three months of learning the modding tools.
To start a youtube channel you need to have a likeable personality, know how to record your gameplay and upload videos.
What group do you think will be willing to work for peanuts?