The fiat on and off ramps (centralized exchanges) are regulated and partnered up with regulated banks and they are all forced to kyc the shit out of anyone converting between the two currencies, and they charge fees.

What you seemed to essentially be seeking is a free peer to peer mode of fiat to bitcoin conversion or vice versa, which is a p2p exchange like robosats, but still that usually involves an institution/company for the fiat side of the deal (because fiat is slavery/control money and sending value over the internet is core to what bitcoin solves). Plus there is generally a premium for those offers anyway, but at least it goes to the person directly.

The other mode would be a physical cash exchange in meatspace. Obvious cons include probably a premium, few opportunities, and some risk of physical danger