Basically, some expectation of privacy especially in a 1-on-1 conversation, even if it's via telecommunications tech rather than in-person.
Some people adopt a more filtered, cautious way of speaking anyway as a defense mechanism. For them it doesn't matter so much. Other people talk informally with less of a filter, and for them it matters quite a bit.
Given that recording is ubiquitous now anyway, and voice deepfakes are about to render even that irrelevant, there probably isn't a good argument against 1-party consent today.
(However, government officials, outside of a foreign policy context, deserve no privacy for anything related to their official duties. The argument that they need to be able to talk informally with their peers, without fear of public judgment, works against the public interest far more than it works for it. That helps build rapport, but no politician these days would fully trust someone they're just building rapport with; that kind of thing may be valuable for diplomatic relations and spies, but not for regular government officials. Privacy and secrecy among ordinary politicians is little more than a recipe for corruption and side-dealing that they know the public would be rightly upset about.)