Politicians don't want to wade into porn regulation because saying anything other than "we will outright ban it" will be construed as condoning something a large population chunk sees as immoral in all circumstances. And, obviously, an outright ban will upset the other large set of the population who has no moral qualms with porn.

Prostitution has exactly the same problem. Legislation that regulates sex work would be seen as condoning sex work. So instead, it's outright banned, which pushes sex work into a black market which endangers the sex workers and their patrons.