I don't think it's really axiomatic that "conservatives hate marijuana", it's more just the case that in a lot of the west, there there are a lot of cultural and identity affiliations, and a lot of simple inertia, which cause much of the right to be opposed to sensible drug policy. Most of the support for the ongoing criminalisation of personal possession of drugs is pretty much mindless status quo bias and not liking the left and progressivism in general.
We've seen this very clearly locally here in the ACT. The Labor-Greens coalition government here legalised cannabis (possession and growing but not sale) in 2019, after the previous position of three decades of decriminalisation. Since the early 1990s the conservative Liberals had been satisfied with cannabis decriminalisation, ie possession and small growing only attracting token non criminal fines, even though in much of the country including the largest cities and states, cannabis remains criminalised under both Labor and the Liberals. At no point did the conservatives here ever suggest they wanted to properly roll this advancement back and re-criminalise cannabis. Status quo was fine for them.
So when cannabis was legalised, the Liberals initially opposed it of course. Then just a year later, at the election, they declared reversing it wasn't a priority. Once the new status quo of possession and small growing legality was established, suddenly they stopped opposing the thing they previously opposed, when it was a proposed reform and not the settled reality.
As well as often coming to quickly tolerate any advances in sensible drug policy once they become the status quo, when pressed, conservative/right wing defences of the ongoing criminalisation tend to be incoherent, inconsistent or focused on side issues which aren't actually about whether personal use of cannabis or other drugs risks a heavy fine or prison sentence.
After the cannabis reforms, we've just had possession decriminalisation laws passed here for most drugs as well. Further sensible progress that's way ahead of the rest of the country. One of the big complaints from the Liberals and cop union about this has been drug driving enforcement. Which makes no sense because it's already illegal to drive under the influence of drugs and alcohol, and still obviously will be. They can't argue the merits of continuing to apply large fines and criminal records and the threat of jail terms for the mere act of having a couple of MDMA pills, so they bring up unrelated stuff instead, as if the change in possession penalty has any impact on driving under the influence.