One aspect is that it provides the pretext for imperialism except with different window-dressing.

The US doesn't occupy and control parts of South America and especially Mexico by forcing policy and stationing its military there to enforce a system of domination over the subjugated population, instead it creates a collaborative partnership where policy designed to address the problems with drug production and trafficking as well as cartels is developed and enforced with the US spearheading it and these policies are backed up by three-letter agencies who act as a pseudo military occupying force (if not an outright military). It's totally different, see?

Another aspect is that US government agencies can weaponise the drug trade, for example unleashing the crack epidemic on poor people and people of colour or–conversely–to use as political leverage such as how the US occupying forces raised up and protected a poppy based pseudo-narcostate in Afghanistan to create a countervailing force against the Taliban while they were on the back foot and operating mostly as an insurgent force (with some reports from Americans in the armed forces claiming that they would act as private security forces for certain drug operations in Afghanistan), and it is also used as a means to generate dark money to use to fund efforts and programs outside of their remit afforded them by congress and outside of the meagre efforts to scrutinise them. The CIA is the big name in this and the Iran-Contra Affair is the most obvious example. If drugs are scarce and they are dangerous then that drives the price of them way up and so the CIA can do shit like fund paramilitary death squads, coups, and black sites with money that congress and auditors will never ever see.

It's also worth keeping in mind that we should avoid slipping into a sort of vulgar materialist analysis here by presuming that there aren't a lot of different factors that exist, often in contradiction to one another, and the influence of ideology can still be very strong despite capitalism wanting to do what capitalism always does.

Some examples of how ideology holds a firm grip on society and can prevail over the "logic" of capitalism and the basic material factors are ones such as preventing and strictly limiting women's employment until fairly recently, and in a similar vein preventing women from having bank accounts and credit cards or the taboo from a century ago around women smoking in public, and of course legalising gay marriage.

Sometimes the prevailing force isn't necessarily a materialist one but one that is squarely rooted in culture, belief, and custom (i.e. ideology), so it's important to not understate the influence of ideology even as materialists.