Failure to enforce drug prohibition resulted in Qing China having a nationwide addiction epidemic for British opium, resulting in the opium wars, the country's bankruptcy, partial European colonization as well as the so-called "century of humiliation". The effects of this addiction epidemic are still being felt nowadays, e.g. in widespread racism towards Asian people as well as the current opioid epidemic where Chinese-made fentanyl is exported worldwide with the unofficial sanction of the Chinese government.

This is the reason why drug prohibition is a thing, and why many Asian countries have death sentences even for simple possession of narcotics.

You do know it's not police who make these laws, right? It's the politicians that get elected by the people who create these laws.

It's supposed to be rehabilitation, but also it's to stop you from ruining other people's lives

You only get life-ruining time for distribution. Distribution ruins other people's lives, often minors and people who have it rough in life.

All Dealers Are Bastards

The logic, whether or not you agree with it, is that drugs in general are hazardous and can kill or disable you, and they contribute to a black market and all the related crimes of drug trafficking and addiction. So punishments aren’t for drug use but for possession and trafficking.

Edit: to all the downvoters, I’m not advocating for draconian drug laws, I’m just answering OP’s question on why cops and lawmakers have such a policy and the logic behind it.

It's called making an example out of someone.

Edit: Lots of people not understanding how that's exactly what cops and shitheads in power think about sending people on drugs to jail. That's scary.

They are more than happy to send your ass to jail for decades because of minor charges that don't hurt anyone but yourself. You're just a number to these assholes. They will make an example out of you if they can.