> MangaPlus is an official source
Like others have said, they're not a fan-run group. MangaPlus is owned by Shueisha, publisher of just about every Jump magazine you've heard of.
@Indigo and
@ZaxaPac are correct in stating that MD wants to link official (external) sources when possible and to make discovery of these sources easier by acting as a one-stop shop for release notifications.
> Cookie notices and acceptance
I'd wager a majority of corporate-owned websites use cookies in some manner. Not something you can easily get away from. At least you're notified these days -- it was much scarier way back when.
> The reader
Dunno if Shueisha takes recommendations for UI/UX improvements, but if there's a better way for them to present content and functionality, I'm sure they're all ears. Or, try the workarounds/alternatives suggested by others here.