...the public is susceptible to misinformation by bad actors in the
financial system and therefore are protected by the SEC...
The SEC governs fixed laws about financial transfers, disclosures, etc., and investigates illegal acts regarding those laws where there are quantitative facts, i.e. who moved how much money to where, who engaged in information for insider trading, and other situations based on hard evidence. Bad actors are deterred by the fact that can be prosecuted for their crimes by the SEC and other authorities.
Shouldn't... political campaigns be audited for truthfulness?
There is no government authority that audits or regulates political ads and/or claims; such authority or laws would clearly violate the First Amendment to the United States Constitution - Wikipedia as to the government regulating or attempting to control or manipulate free speech.
In a non-partisan fashion, government authorities can and do routinely supply publicly available documents that can be used by the public, fact checkers and the press.
False political claims are investigated by the press and various non-profits, also under the same 1st Amendment protections so that the press can operate free of government intrusion. See https://www.google.com/search?q=political+fact+checking for different political NGOs and media outlets which do fact checking. Such resources themselves can be fact challenged and partisan themselves, of course; news outlets can be under the editorial control of a political agenda, and a "fact checking" website or NGO can be funded by partisans.
...why shouldn't the same be done in the political system?
Within a political system such as the US, people are responsible for their own thoughts and actions; and they are responsible for assessments of what may or may not be factual, and for what they believe (which, of course, can be removed from a factual basis). The idea that a government should be involved in auditing or otherwise having control over political speech is a political question, not a legal question.