Earlier quoted context omitted.
Because your addiction is also your wife's problem, your parent's problem, your company's problem. Addiction affects more than just the addict. And addicts are in need of help - while it is easy to think that "they like being high, it's their choice", in fact the addicts hate their habit more than anything, yet they can't stop using without external help. Would you help a person with a broken leg ? Why ? Well, that's…
Not all addicts are in need of help. And many addicts really do enjoy being high or otherwise find opiates help them through life, work, etc. and do not want to quit. And out of those that do want to quit, I'd bet a large amount of it is due to the high prices the legal scheme enforces. With reasonable prices, the biggest issue with being an opiate user disappears.
Of course addicts enjoy being high. I'd wager essentially all addicts enjoy the high, even if the joy is just the abatement of withdrawal symptoms.
And while some addicts don't want to "quit", that's true, a vanishingly small percentage enjoy being addicted. In my reading and limited first-hand discussions, even those addicts who don't want to quit still wish they could "cut back", e.g., wish they could just be a social drinker or only shoot heroin on the weekends. They hate the powerlessness they feel, hate the control the substance has over their lives.
Lastly, I don't have hard evidence to back this up, but I've never read/heard an addict cite the high price of their drug being the biggest reason to quit. The biggest reason they want to quit is typically either its impact on their health or its impact on their relationships (or career, which is basically a relationship). I'm not saying you're irrefutably wrong about this; it just doesn't match my anecdotal experiences.
The one thing all addicts share is an expert ability to obtain and use their substance. If it is physically possible to get their fix, they will find a way. Also, illegal drugs are often cheaper than legal ones, because regulatory compliance and taxes add more expense than operating in a black market. At least, that's the evidence coming out of states and countries that have recently legalized certain drugs.