You're right, I was missing that they were just hiding the funds for information purposes, not tax purposes. In that case the fine is probably more appropriate.

Filing a 13F is essentially a tax upon all market participants, it provides zero benefit to the public. Filing has a financial cost. If the SEC settlement were less than the cost of filing over multiple years, then all rational actors would stop paying to file 13-Fs and simply pay off the SEC every couple years. The middlemen and the pretend regulators both benefit from busywork continuing, so the fee is slightly more than the cost of filing 13-Fs to encourage cooperation.

There's probably a joke in there somewhere about the 13-F process being "securities theater" as compared to the better known IT "security theater" phrase. 13-F is a classic example of "regulation can sometimes be wasteful and inconvenient" therefore anything wasteful or inconvenient can be hand waved away by appeals to "regulation" much like the classic analogy with computer security. See also security theater at airports, plenty of the governmental covid responses, etc.