It would cost them votes with a certain group of voters who would make this a capital offence if they could.

It doesn’t really impact MPs, see the studies into drug use at the HoP or even this articles headline, so why bother risking losing important votes in swing seats? If the police started throwing MPs in jail for drug use then you’d see something done quite quickly.

Much like a lot of these wedge issues such as abortion there are a few nutters in the HoP who are rabidly opposed to it on moral grounds and a few whose husbands own legal medical cannabis farms who frankly don’t want the competition.