Because most insider trading is trivial to catch. An insider trader has to act ex ante. That's difficult on multiple levels: acquisition of the information, predicting its effect and executing the trades all while evading capture. Detection, on the other hand, is ex post facto: find unusually profitable trades after the information has occurred. That's what the SEC does. To the extent insider traders aren't caught, it's because they failed to turn a profit.

Look at the people being caught insider trading; they're rarely professionals. Because professionals know how hard it is relative to the gains. Instead, it's mostly numpties who heard about an acquisition from their spouse or whatever.

With crypto, we have the tape. But linking the wallets to the numpties is hard. (Also fewer people care about the victims, let's be honest.) Imagine if this chain had real names attached to it. We'd have a predictable list of offenders to prosecute.