To understand why this isn't a conspiracy of a sort by some "elite" group of people to take money from 401ks and IRAs, you'd have to argue that there's a good reason to shorten the window that outweighs the reason the window exists. The fact remains that many many IPOs crater within a few months. The rule change seems to exist to leave small low-effort investors holding the bag.
Just because we're paranoid doesn't mean they're not out to get us.
It's also not hard to think of half a dozen other groups that could possibly benefit and plausibly have enough clout to steer things in their favor, hence why the need to make a specific claim rather than beating around the bush a vague "they" that can't be refuted.
It isn't central to the discussion. The appearance of corruption is clear; nailing down the culprit is difficult. It isn't reasonable to expect people to have a theory of corruption in order to complain about it.
>Otherwise this is just generic conspiratorial thinking
The perception of corruption is not a conspiracy theory. Corruption is an ordinary financially motivated crime, while conspiracy theories usually involve some kind of grandiose or mystical objective ("new world order").
Anyway, the question is moot because the only possible answer is "the regulatory authorities". We know who makes the rules! I just didn't want to tolerate this kind of fallacious nitpicking.