Main Reasons:
More reason for Epic Games Store not to improve their launcher and securities, while keeping more and more money to buy exclusivity. It is wise for GOG Galaxy 2.0 to have Epic Games Launcher to integrate? Bad Move and next level scummier and unethical move from Tim Sweeney.
https://twitter.com/TimSweeneyEpic/status/1139655680506417152

Optional reasons:
Edit: And possible Spying on all different launchers.

If CD Projekt Red is real stupid enough to let that happen.

The only reason I should be rolling this much is if my hands are spilling forth a set of dice.

Unfortunately, all you've got rolling on me is my eyes.

The whole point of the 2.0 thing is to integrate all your client accounts together. If they ignore one because some undefined percentage of people don't like it, it ruins the whole point. Don't want to integrate Epic's store into GOG 2.0? Simply don't make an account there or add it to Galaxy. Simple.

But that would make too much sense, doesn't it?

GOG Galaxy 2.0 was created for the sole purpose of combining every launcher into one. Not having EGS would be stupid even tho most people like to hate on them. If you don't want Epic's launcher to spy on you then don't use it and let people make their own choice.

I loved the integration, it worked like a charm. Well done GOG team!

Huh, a necro. Before I spotted the age of the thread I kind of assumed this was about the more recent EGS deal about being able to buy from EGS within Galaxy.