With weed, what the Dutch model tries to achieve is to not punish people for smoking weed, but also not turn it into a for-profit industry that would create an incentive to get more people addicted.
It’s more that there’s a lot of conservative parties that do not agree on the drug policy. E.g. enough Christian parties who would rather be more restrictive.
This is the reason that legalization in Belgium isn’t even remotely on the table. AB Inbev practically writes the law here.