The early proto-EU was not "policed". By the time of the Star Wars Renaissance of the 1990s, the publishers and LucasArts and staffers at Lucasfilm were working to actively make sure all the new EU content meshed, and were finding ways to massage older contradictory material. Things didn't get problematic until Episode I, when George not only reserved the right to ignore or use anything in the EU (he liked Tim Zahn's name for the pre-Empire capitol, and used it) but contradicted his own lore, notes, and commentary. Still no real problems until Episode II, when he utterly steamrolled all of the EU material about Boba Fett, and the tie-in authors had to madly jig to come up with rationalizations to make it all work. But they did. Episode III really threw a wrench into the lore, with the drawn out events -- as previously established by George in his commentary and notes -- of the Clone Wars (plural), dissolution of the Jedi, declaration of Empire, death/fall of Anakin, birth of the twins, and death of Padmé... all now take place on the same day. But it still didn't over-write most of the EU or the characters therein. So yeah. We felt "safe", if you will.
Then Clone Wars came along, and completely reconceptualized Mandalore and the Mandalorians. That was just after the Story Group was formed, and one wonders what they made of that vis-a-vis their role. Even then, there followed another five years of lore-building, with the EU still largely intact, rationalized, and otherwise "certain point of viewed" into something resembling how it had started out. It really was only with the sale of Lucasfilm to Disney that things changed drastically. First there was the one-two punch of them declaring the EU "Legends", and invalidating all the post-ROTJ stories and characters (and messing with a nonzero number of PT/OT-era characters and stories, too), coupled with the justification of "one canon". To have them then not follow that big assertion, it feels a bit like, "Well, then, why'd you bother to wipe out the EU when not even your precious new canon is safe"?
It wasn't that Lucasfilm reserved the right to ignore anything in the EU. It's that they largely didn't, but now that everything is supposedly equally sacrosanct, they're contradicting ancillary content left and right.