Low Culture, High Tech: Happens an awful lot, due to the absence of any Alien Non-Interference Clause, and the common interpretation of general free trade statutes by free traders as “can (and will) sell anything to anybody who wants it”. If they don’t read the manual (or, in many cases, the encyclopedia) – well, at least what happens subsequently is unambiguously their own damn fault, and they haven’t a leg to stand on if they come back to you in the future to bitch about it, unlike the problems that arise if you try to play regulator to their technological development.
(More sensible low-tech societies go out and hire some professional uplift consultants to avoid this biting them on the ass too hard.)
Alien Non-Interference Clause: “Ha ha ha ha ha ha ha ha no… wait, you were serious?”
The Associated Worlds in general think they have a good handle on precisely what this sort of “Prime Directive” would mean in practice. Namely, it would mean that the first time one of those “protected” pre-spaceflight civilizations got out into the black and found out about the people who’ve cheerfully been sitting up there in the sky watching them struggle through all kinds of preventable sickness and disaster and suffering and death in the name of the naturalistic fallacy, they’re going to go home and report that the Galaxy is full of utter, unprintable, callous bastards. And then things will not go so well in the field of interstellar relations.
Plus, of course, there are plenty of less scrupulous civilizations out there than the mainstream Great Powers of the Associated Worlds. Their term for protected-by-non-interference-rules pre-spaceflight civilizations is “easy meat”. Whole planets full of marks! (“We are the Great Star Gods!”… or “We blew that city off the map as a demonstration. Have ten million tons of $RESOURCE ready when we come back in a year, or we’ll blast ten next time.”) Walking snacks! Pets! Toys! Culture dishes! Reality television! (Which, in some cases, means real, live-action war movies.)
Et cetera. Ignorance is not bliss, and indeed is fairly likely to get you killed.
(There are “protected planets” that are hands-off under the Accord on Protected Planets, but in those cases, it’s usually because one of the Powers has an interest in the locals, or the people they transplanted there, and for that matter, the protecting power generally reserves the right to interfere more or less at its own discretion.)