Except simply accessing a tool doesn’t improve anyone’s gameplay experience. Okay, so there is a menu item for viewing killmails - what does it do? Why is it relevant? How do you use it, and what are the pros and cons of its data set? Also, how do players control whether their killmails are accessible to others? Does it opt in by default, or is it locked down and you have to edit permissions to make your killmails accessible?
How does having it in-game answer any of those questions, or help a player use it?
Once you put the tools inside the game, CCP has to maintain them, create and maintain instruction materials for them, and update them alongside all the other code maintenance that goes into every release. Whereas when they are out of the game, not only can they not possibly break other components of EVE, they can be independently updated and improved upon without waiting for CCP to decide to spend money on a tiny aspect of their game engine. Just look at the fitting tool that is already in EVE - it’s 4 years old and has been hardly touched.
I would much rather the tools remain outside EVE where they can continue to be developed, than get shoehorned into EVE and left to languish.
But I do agree that the existence of useful out-of-game content needs to be better promoted during the NPE - including these forums, which tons of players are utterly unaware of.